Tumor Biologics

2. Obesity and Cancer Risk

• Historically, obesity has been linked to diabetes and cardiovascular disease but less attention has been given to its relationship with cancer.
• Epidemiological studies link obesity to multiple cancers, including:
  • Esophageal cancer
  • Colorectal cancer
  • Gallbladder cancer
  • Pancreatic cancer
  • Liver cancer
  • Gastric cancer
  • Postmenopausal breast cancer
  • Uterine cancer
  • Ovarian cancer
  • Renal cell carcinoma
  • Meningioma
  • Multiple myeloma
  • Thyroid cancer
• Globally, increased BMI is the third most significant risk factor for cancer, following infection and smoking.
  • Obesity contributes to up to 20% of cancer-related deaths.
• Bariatric surgery has shown promise in reducing cancer risk by 33% in obese patients compared to weight-matched controls.

3. Physical Activity and Cancer

• Decreased physical activity has been linked to an increased incidence of various cancers.
• Protective effect of exercise:
  • Esophageal adenocarcinoma (HR: 0.58)
  • Gallbladder cancer (HR: 0.72)
  • Liver cancer (HR: 0.73)
• 13 out of 26 cancer subtypes showed decreased rates in individuals engaging in moderate to vigorous physical activity.
  • Significant even after adjusting for BMI.
• Physical activity is associated with an increased risk of:
  • Melanoma (HR: 1.27)
  • Prostate cancer (HR: 1.05)
• Dose-dependent relationship observed for colorectal adenocarcinoma and physical activity.
• Sedentary behavior linked to:
  • Increased overall cancer incidence
  • 20% increased cancer mortality in the least active individuals.

Stepwise Progression from Melanocyte to Metastatic Melanoma

Step	Characteristics
1	Common melanocytic nevus
2	Dysplastic nevus
3	Radial growth phase of melanoma
4	Vertical growth phase of melanoma
5	Metastatic melanoma

Notes:

• Common acquired and congenital nevi without cytologic atypia (step 1) may progress into dysplastic nevi with clear atypical histologic and cytologic features (step 2).
• Most of these lesions are stable, but a few may progress to a malignant melanoma that tends to grow outward along the radius of the plaque (step 3).
• Within the plaque, fast-growing cells expand in a vertical direction (step 4), invading the dermis and elevating the epidermis.
• Finally, the tumor metastasizes (step 5).

Key Physiologic Changes in Tumor Cells (Hallmarks of Cancer)

1. Sustaining proliferative signaling
   • Tumor cells maintain continuous signals to keep proliferating.
2. Evading growth suppressors
   • Tumor cells bypass growth-inhibitory signals.
3. Avoiding immune destruction
   • Tumor cells escape detection and destruction by the immune system.
4. Enabling replicative immortality
   • Tumor cells can undergo an infinite number of divisions.
5. Tumor-promoting inflammation
   • Chronic inflammation in the tumor microenvironment aids in cancer progression.
6. Activating invasion and metastasis
   • Tumor cells gain the ability to spread and invade distant tissues.
7. Inducing angiogenesis
   • Tumor cells stimulate new blood vessel formation to supply nutrients.
8. Genome instability and mutation
   • Tumor cells acquire mutations that accelerate evolution and adaptation.
9. Resisting cell death
   • Tumor cells evade mechanisms that typically cause cell death (apoptosis).
10. Deregulating cellular energetics
11. Tumor cells alter their energy production processes to meet increased demand.

Biomarkers and Biologically Targeted Therapies

Cancer	Biomarker	Therapy (Class)
Breast	BRCA	Olaparib (PARP inhibitor)
Breast	Estrogen/progesterone receptor	Tamoxifen (Selective estrogen receptor modulator) / Letrozole (Aromatase inhibitor)
Breast	HER2/neu	Trastuzumab (antiHER2)
Chronic myelogenous leukemia	bcr-abl	Imatinib (Tyrosine kinase inhibitor)
Colorectal cancer	KRAS	Cetuximab (antiEGFR)
Colorectal cancer (tumor agnostic)	MSI	Pembrolizumab (antiPD1)
Gastrointestinal stromal tumor	c-kit	Imatinib (Tyrosine kinase inhibitor)
Lymphoma	CD20	Rituximab (antiCD20)
Melanoma	BRAF	Dabrafenib (antiBRAF) + Trametinib (antiMEK)
Non-small cell lung cancer	ALK or ROS1	Crizotinib (Tyrosine kinase inhibitor)
Non-small cell lung cancer	EGFR	Gefitinib (Tyrosine kinase inhibitor)
Non-small cell lung cancer	PD-L1	Pembrolizumab (antiPD1)

Key Notes:

• Biomarkers are increasingly used to guide the decision of which patients should receive biologically targeted therapies, often independent of formal staging criteria.
• Examples include various cancers, such as Breast Cancer, Lung Cancer, and Melanoma, where specific biomarkers (e.g., HER2, BRCA, ALK) are associated with targeted therapies (e.g., Trastuzumab, Olaparib, Crizotinib).

Cell Cycle Overview and Regulation

Key Phases of the Cell Cycle:

1. G₁ (Gap 1 Phase):
   • Prepares the cell for DNA synthesis.
   • Checkpoint: Decision to proceed to S phase or enter G₀ (quiescent state or terminal differentiation).
2. S (Synthesis Phase):
   • DNA replication occurs.
3. G₂ (Gap 2 Phase):
   • Prepares the cell for mitosis.
4. M (Mitosis):
   • Cell division into two daughter cells.
5. G₀:
   • Cells can enter a quiescent state or become terminally differentiated.

Key Checkpoint: G₁ to S Transition

• Critical control point in the cell cycle.
• Cells are committed to division once they pass this checkpoint.

Molecular Regulators:

• Cyclins and CDKs (Cyclin-dependent kinases) drive progression through the cell cycle.

Tumor Suppressors and Oncogenes:

• Tumor suppressors:
  • p53 and Rb (retinoblastoma protein) block the G₁ to S transition to prevent uncontrolled cell division.
• Oncogenes:
  • Cyclin D1 and E2F promote the transition from G₁ to S, pushing the cell into division.

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Resisting Cell Death in Tumors

Overview of Tumor Growth and Cell Death

• Tumor growth is influenced by the balance between cell proliferation and cell death.
• Apoptosis, a form of programmed cell death, is crucial for maintaining tissue homeostasis and regulating tumor growth.
• Tumor cells often have defects in cell death signaling pathways, making them resistant to apoptosis.

Apoptosis: The Main Form of Cell Death

• Apoptosis is essential for:
  • Embryonic development
  • Immune system function
  • Tissue homeostasis
• Key features of apoptosis:
  • Disruption of membranes
  • Chromosomal degradation within hours
  • Caspase activation cascade leading to DNA fragmentation and cell death

Apoptosis Pathways

1. Extrinsic Pathway (Death Receptor-Dependent)
   • Triggered by death receptors like:
     • Fas receptor
     • Death receptor 5 (DR5)
   • Ligands: Fas ligand and TRAIL bind to these receptors.
   • Activates caspase 8 → leads to apoptosis.
2. Intrinsic Pathway (Receptor-Independent)
   • Triggered by cellular stress such as:
     • Growth factor withdrawal
     • Hypoxia
     • DNA damage
   • Proapoptotic molecules cause mitochondrial damage → release of cytochrome c.
   • Cytochrome c activates caspase 9 → activates caspase 3 → apoptosis.

Molecular Alterations in Cancer

• Bcl-2 oncogene:
  • Discovered in B cell lymphomas.
  • Prevents apoptosis, leading to lymphocyte survival.
• p53 tumor suppressor:
  • Inactivated in over 50% of human cancers.
  • Normally, p53 senses DNA damage and triggers apoptosis.
  • Loss of p53 leads to resistance to apoptosis in cancer cells.
• Phosphatidylinositol 3-kinase/AKT pathway:
  • Transmits antiapoptotic survival signals.
  • Activated by IGF-I, IGF-II, or IL-3, as well as Ras mutations or loss of PTEN.
• Decoy Receptors:
  • Example: DcR1, DcR2, osteoprotegerin, and DcR3 neutralize death-inducing ligands like TRAIL and FAS ligand, promoting tumor survival.

Non-Apoptotic Cell Death Mechanisms in Tumors

1. Necrosis:
   • Induced by pathophysiologic conditions such as inflammation and ischemia.
   • Results in unregulated cell destruction and proinflammatory signals.
   • Promotes tumor growth by inducing angiogenesis, immune suppression, and metastasis.
2. Autophagy:
   • Triggered by nutrient limitation (e.g., hypoxia, DNA damage).
   • Helps tumor cells survive under stressful conditions.
   • Particularly important in RAS-mutated cancers (e.g., pancreatic, lung, and colon cancers).
3. Ferroptosis:
   • Iron-dependent cell death caused by accumulation of lipid peroxides.
   • Excessive ROS damages lipids and proteins, leading to cell death.
4. Mitotic Catastrophe:
   • Occurs due to failed mitosis in cells with DNA damage.
   • Leads to cell death when the G₂ checkpoint fails to block mitosis.

Senescence: Growth Arrest in Tumor Cells

• Senescence occurs when damaged cells lose their ability to divide (clonogenicity) but fail to undergo cell death.
• Defects in the senescence program contribute to tumor development.

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Deregulating Cellular Energetics and Metabolomics in Cancer

1. Overview of Cellular Metabolism in Cancer

• Otto Warburg originally described the phenomenon where cancer cells predominantly undergo glycolysis even in the presence of oxygen—known as the Warburg effect.
• Glycolysis is less efficient, providing much less energy than oxidative phosphorylation, yet cancer cells enhance glycolysis rates dramatically (up to 200 times that of normal cells) to meet their energy needs.

2. Mechanisms of the Warburg Effect

• Cancer cells increase glycolysis by upregulating glucose transporters like GLUT1.
• This high rate of glycolysis is exploited clinically; for example, positron emission tomography (PET) using 18F-fluorodeoxyglucose highlights increased glucose uptake by tumors.

3. Classes of Metabolic Reprogramming in Cancer

• Transforming Activities: Directly contribute to cancer cell transformation.
  • Mutations in enzymes like IDH1, IDH2, succinate dehydrogenase, and fumarate hydratase disrupt the citric acid cycle.
  • These mutations lead to the accumulation of oncometabolites (e.g., 2-hydroxyglutarate, succinate, fumarate) which impair critical cellular functions like DNA and histone demethylation.
• Enabling Activities: Support the cancerous state but do not directly cause transformation.
  • For example, mutations in KRAS enhance nutrient acquisition and macromolecule synthesis, essential for tumor growth and survival.
  • Targeting these pathways can inhibit tumor growth, particularly in KRAS-driven cancers.
• Neutral Activities: Metabolic functions in cancer cells that are not essential for their growth or survival.

4. Implications for Cancer Treatment

• The field of metabolomics in cancer research focuses on understanding these metabolic changes to identify new therapeutic targets.
• Current research includes:
  • Clinical trials for drugs targeting IDH1 and IDH2 mutations.
  • Exploration of treatments targeting specific amino acids, like arginine in hepatocellular carcinoma (HCC), which are crucial for cancer progression.

5. Future Directions

• This rapidly evolving research area holds significant potential for developing new cancer therapies by targeting specific metabolic pathways altered in cancer cells.
• The ongoing studies and trials are just beginning to tap into the possibilities of metabolomics in oncology, indicating a promising future for targeted cancer therapies.

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Genetic Model for Colorectal Tumorigenesis

1. Chromosomal Alterations and Gene Mutations:
   • 5q mutation or loss:
     • Gene affected: FAP (Familial Adenomatous Polyposis, APC gene)
     • Linked to the transition from normal epithelium to hyperproliferative epithelium.
   • 12p mutation:
     • Gene affected: K-Ras
     • Drives the progression from hyperproliferative epithelium to early adenoma.
   • 18q loss:
     • Gene affected: DCC (Deleted in Colorectal Cancer)
     • Contributes to the transition from intermediate adenoma to late adenoma.
   • 17p loss:
     • Gene affected: p53
     • Leads to the transformation from late adenoma to carcinoma.
2. Progression of Tumorigenesis:
   • Normal epithelium → Hyperproliferative epithelium (due to loss of FAP gene)
   • Early adenoma → Intermediate adenoma (due to mutations in K-Ras)
   • Late adenoma → Carcinoma (due to the loss of p53 and other chromosomal alterations)
   • Final progression: Metastasis
3. Key Genetic Events:
   • DNA hypomethylation plays a role in the progression from hyperproliferative epithelium to early adenoma.
   • Aneuploidy and chromosomal deletions in 5q, 12p, 18q, and 17p are significant drivers of tumor progression.
   • Accumulation of multiple gene alterations drives the transition from benign adenomas to malignant carcinoma and eventual metastasis.

Familial Cancer Syndromes

Selected Familial Cancer Syndromes:

Retinoblastoma

Overview

• Retinoblastoma is a pediatric retinal tumor, often detected by the age of 5 years (95% of cases).
• Bilateral disease is generally manifested within the first year of life.
• Associated with extraocular malignant neoplasms such as:
  • Sarcomas
  • Melanomas
  • Tumors of the central nervous system

Genetics of Retinoblastoma

• RB1 gene: The first tumor suppressor gene to be cloned.
  • Retinoblastoma holds historical significance in cancer genetics due to its association with the RB1 gene.
• Hereditary vs. Sporadic Forms:
  • Hereditary retinoblastoma: Germline mutation in about 40% of cases.
  • Sporadic retinoblastoma: Arises due to somatic mutations.

Knudson’s Two-Hit Hypothesis

• Hereditary retinoblastoma:
  • Two mutations are required for tumor development:
    1. One germline mutation (inherited).
    2. One somatic mutation (acquired during life).
  • Children with an affected parent typically develop bilateral tumors.
• Sporadic retinoblastoma:
  • In unilateral cases with no family history, both mutations are somatic.
• The hypothesis explains that both hereditary and nonhereditary forms of retinoblastoma require two genetic events for tumor development.

RB1 Protein

• RB1 protein: A key regulator of the cell cycle.
  • Its loss results in the failure of retinoblasts to differentiate properly, leading to tumorigenesis.

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Li-Fraumeni Syndrome

Overview

• First described in 1969 by Li and Fraumeni.
• Involves a broad range of cancers, including:
  • Sarcomas (soft tissue and bone)
  • Breast cancers (most common malignant neoplasm)
  • Brain tumors
  • Leukemias
  • Adrenocortical carcinomas
  • Various other cancers

Chompret Criteria

Four clinical scenarios to suspect Li-Fraumeni syndrome and offer genetic counseling/testing:

1. Proband diagnosed with a Li-Fraumeni spectrum tumor before age 46, with at least one first or second degree relative having a Li-Fraumeni tumor.
2. Proband with multiple malignancies, of which at least two are Li-Fraumeni-associated, diagnosed before age 46.
3. Patients with adrenocortical carcinoma, choroid plexus carcinoma, or embryonal anaplastic rhabdomyosarcoma (irrespective of family history).
4. Breast cancer before age 31 years.

Genetics

• Approximately 70% of Li-Fraumeni kindreds have mutations in the TP53 gene.
• TP53 gene produces the p53 protein, a key tumor suppressor.
• Inheritance: Autosomal dominant.
• Penetrance:
  • 50% by the age of 31 in females.
  • 50% by the age of 46 in males.
  • Nearly 100% by the age of 70.

Sensitivity to Radiation

• Patients with Li-Fraumeni syndrome exhibit increased sensitivity to radiation.
• New malignant neoplasms may develop in the irradiated field.

Non-TP53 Genetic Factors

• In families without germline TP53 mutations, potential candidate genes include:
  • CHK1 and CHK2 (cell cycle checkpoint kinases) which phosphorylate p53.
• Other possible factors:
  • Telomere length alterations in the p53 gene.
  • Aberrant gene methylation.
  • Variant microRNAs that regulate p53.
  • Accumulation of copy number variants.

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Familial Adenomatous Polyposis (FAP) and Related Polyposis Syndromes

Familial Adenomatous Polyposis (FAP)

• Prevalence: Accounts for ∼1% of all colorectal cancer cases.
• Genetics: Autosomal dominant condition caused by mutations in the APC gene, located on chromosome 5q21.
  • Penetrance: Approaches 100% for colorectal cancer by age 50.

Clinical Features of FAP

• Development of hundreds to thousands of adenomatous polyps in the colon.
• Polyps emerge typically in the second and third decades of life.
• Risk of colorectal cancer is extremely high due to the number of polyps rather than individual polyp behavior.
• Untreated individuals typically present with colorectal cancer by age 35–40.

Extracolonic Manifestations

• Upper gastrointestinal polyps:
  • Nearly 100% of cases develop duodenal adenomas.
  • 10% develop gastric adenomas.
  • 20%-84% develop fundic gland polyps.
• Desmoid tumors: Occur in 15% of cases (locally invasive fibromatoses in the abdomen or abdominal wall).
• Other manifestations:
  • Thyroid cancer (2%-3%, typically papillary)
  • Congenital hypertrophy of the retinal pigment epithelium (70%-80%)
  • Fibromas (25%-50%)
  • Epidermoid cysts (50%)
  • Osteomas (50%-90%)
  • Dental abnormalities

Molecular Pathogenesis

• APC Gene: Encodes a 300-kDa protein involved in cell adhesion and migration.
  • Role: Regulates phosphorylation and degradation of β-catenin through the Wnt signaling pathway.
  • APC mutation leads to β-catenin accumulation → alters gene expression → impacts cell proliferation and apoptosis.
• Over 700 mutations identified in APC:
  • Frameshift mutations (68%)
  • Nonsense mutations (30%)
  • Large deletions (2%)
  • Mutation cluster region: 5' end of exon 15.
  • Phenotypic variations:
    • Profuse FAP: Mutations between codons 1250–1464.
    • Intermediate [Classic phenotype] FAP: Mutations between codons 157–1595.
    • Congenital hypertrophy of the retinal pigment epithelium: Mutations between codons 311–1465.

Gardner Syndrome

• A variant of FAP associated with:
  • Osteomas of the mandible or skull.
  • Epidermal cysts.
  • Desmoid tumors and thyroid tumors.

Attenuated FAP (AFAP)

• Phenotypically distinct variant of FAP:
  • Fewer than 100 adenomas.
  • Proximal colon distribution of polyps.
  • Colorectal cancer onset is ∼15 years later than classic FAP.
• Mutations occur in the upstream or downstream regions of the APC gene.

MYH-Associated Polyposis (MAP)

• Genetics: Caused by mutations in the MYH gene, inherited in an autosomal recessive pattern.
  • Heterozygotes: 3-fold increased risk for colorectal cancer.
  • Biallelic carriers: 50-fold increased risk.
• Phenotype:
  • Fewer than 100 polyps.
  • Mean age of diagnosis: 50 years.
  • Polyps distributed throughout the colon.
• Extracolonic manifestations: Similar to those in FAP.
• Mutations:
  • Y179C on exon 7.
  • G396D on exon 13 (∼80% of cases).
• MYH gene encodes DNA glycosylase, involved in base excision repair to prevent mutations from oxidative damage.
• Aneuploidy: MYH mutations lead to chromosomal instability and aneuploidy, which is an early event in both FAP and MAP tumors.

This summary covers the clinical presentation, molecular pathogenesis, and genetic variations of FAP, Attenuated FAP, and MYH-Associated Polyposis.

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Hereditary Nonpolyposis Colorectal Cancer (HNPCC / Lynch Syndrome)

Overview

• Prevalence: Accounts for 2%-3% of all colorectal cancers.
• Genetics: Autosomal dominant condition caused by mutations in DNA mismatch repair genes.
• Phenotype:
  • Right-sided colonic cancers.
  • Earlier onset, with a median age of diagnosis around 45 years.
  • Increased likelihood of synchronous and metachronous cancers.

Colorectal Cancer Progression

• Adenomatous polyp incidence is the same as in sporadic cases.
• Accelerated carcinogenesis:
  • Tumors progress from adenoma to carcinoma in 2-3 years (compared to 8-10 years for sporadic cases).
  • Due to a higher mutation rate in HNPCC tumors (2-3 times higher than normal cells).

Microsatellite Instability (MSI) and DNA Mismatch Repair

• MSI-H (Microsatellite Instability-High):
  • Caused by mutations in DNA mismatch repair (MMR) genes.
  • MMR genes affected in HNPCC include:
    • MSH2
    • PMS2
    • MLH1
    • MSH6
    • MSH2 promoter hypermethylation (linked to EPCAM mutation).
• Microsatellites are regions where short DNA sequences are repeated, and replication errors can lead to mutations.
• DNA Mismatch Repair proteins fail to correct these errors, leading to inactivation of tumor suppressor genes.

Lifetime Risk and Phenotypic Variations

• Lifetime risk of colorectal cancer:
  • Nearly 70% in males.
  • Just over 50% in females.
• Specific gene mutations affect cancer risk:
  • MLH1, PMS1, and MSH2 mutations confer a higher lifetime risk of colorectal cancer.
• MSI in sporadic colorectal cancer:
  • Occurs in 15% of sporadic cases.
  • Caused by methylation silencing of the MLH1 gene (not mutations like in HNPCC).

Extracolonic Cancers in HNPCC

• Endometrial cancer
• Ovarian cancer
• Urinary tract cancer
• Small bowel cancer
• Stomach cancer

Current Testing and Treatment

• MSI testing is recommended for all newly diagnosed colorectal and endometrial cancers.
• MSI-H tumors have shown remarkable response to anti-programmed death receptor-1 (PD-1) immunotherapy due to their high mutational burden.
• In 2017, pembrolizumab became the first tumor type agnostic drug approved for treating metastatic MSI-H tumors.

This summary highlights the key aspects of HNPCC (Lynch Syndrome), focusing on its genetic basis, accelerated tumorigenesis, associated extracolonic cancers, and current therapeutic advances using immunotherapy for MSI-H tumors.

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BRCA1 and BRCA2 in Hereditary Breast and Ovarian Cancer

Prevalence and Risk

• 5%-10% of all breast cancers are hereditary.
• Primarily linked to mutations in BRCA1 and BRCA2 genes, especially common in people of Ashkenazi Jewish descent.
• In families with a history of hereditary breast and ovarian cancer, 90% of cases are attributable to BRCA1 or BRCA2 mutations.

Cumulative Risk of Breast and Ovarian Cancer

• BRCA1 carriers:
  • 72% risk of breast cancer by age 80.
  • 44% risk of ovarian cancer by age 80.
• BRCA2 carriers:
  • 69% risk of breast cancer by age 80.
  • 17% risk of ovarian cancer by age 80.

Other Associated Cancers

• BRCA1 and BRCA2 carriers:
  • Male carriers: Increased risk of prostate cancer.
  • BRCA2 is more commonly associated with male breast cancer.
  • BRCA2 also linked to higher risks of:
    • Melanoma
    • Pancreatic cancer (6.2 times increased risk)
    • Stomach cancer
    • Gallbladder and biliary cancers

Genetics and Molecular Function

• BRCA1:
  • Located on chromosome 17.
  • 100,000 nucleotides with numerous mutations (most are frameshift or nonsense mutations that result in truncated proteins).
• BRCA2:
  • Located on chromosome 13.
  • Larger gene compared to BRCA1, also with common frameshift or nonsense mutations.
• Both BRCA1 and BRCA2 are tumor suppressor genes involved in:
  • DNA damage repair
  • Regulation of gene expression
  • Cell cycle control
• Following the Knudson two-hit hypothesis, one allele is inherited with a mutation, and the second allele is inactivated in tumor cells, leading to cancer.

Phenotypic Variations Based on Mutation Location

• Specific mutations on BRCA1 and BRCA2 confer different cancer risks:
  • BRCA1 c.68_69delAG mutation (common among Ashkenazi Jews):
    • 84% risk of breast cancer by age 70.
  • Other mutations on BRCA1 (e.g., c.2282 to c.4071):
    • Lower risk, 56% risk of breast cancer by age 70.

This summary highlights the hereditary risk associated with BRCA1 and BRCA2, their roles as tumor suppressor genes, and their links to a wide spectrum of cancers beyond breast and ovarian cancers.

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Multiple Endocrine Neoplasia Type 1 (MEN1)

Overview

• Inheritance: Autosomal dominant.
• Characterized by:
  • Parathyroid tumors → leading to hyperparathyroidism.
  • Pancreatic islet cell tumors.
  • Pituitary gland tumors.

Additional Manifestations

• Lipomas
• Adenomas of the adrenal and thyroid glands.
• Cutaneous angiofibromas
• Carcinoid tumors

Genetics

• Caused by mutations in the MEN1 gene located on chromosome 11q13.
• Menin: The protein product of the MEN1 gene, found predominantly in the nucleus.
  • 80% of mutations lead to the loss of function of menin.
  • Menin binds to proteins involved in:
    • Transcription regulation
    • DNA repair
    • Cytoskeleton organization
  • However, none of these pathways has been conclusively linked to MEN1-related tumorigenesis.

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Multiple Endocrine Neoplasia Type 2 (MEN2)

Overview

• Inheritance: Autosomal dominant.
• Characterized by:
  • Medullary thyroid carcinoma (MTC) – occurs in all affected individuals.

Subtypes

1. MEN2A:
   • Pheochromocytoma (50% of cases).
   • Hyperparathyroidism (25% of cases).
2. MEN2B:
   • MTC and pheochromocytoma.
   • Mucosal neuromas on the tongue, lips, and subconjunctival areas.
   • Intestinal ganglioneuromatosis.
   • Marfanoid body habitus.
   • Majority of cases arise from spontaneous new mutations in RET.

Genetics

• Caused by mutations in the RET proto-oncogene located on chromosome 10q11.
• The RET gene encodes a transmembrane tyrosine kinase receptor expressed on neuroendocrine and neural cells, including:
  • Thyroid C cells
  • Adrenal medullary cells
  • Autonomic ganglion cells
• Mutations in the RET gene lead to constitutive activation of signaling pathways:
  • p38/MAPK pathway
  • JNK pathway

This summary covers the key characteristics of MEN1 and MEN2, including the clinical features, genetic causes, and the molecular mechanisms driving these endocrine neoplasias.

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Von Hippel–Lindau Syndrome (VHL)

Overview

• Inheritance: Autosomal dominant.
• Incidence: Affects approximately 1 in 35,000 live births.
• Characterized by the development of highly vascularized tumors in multiple organs.

Associated Tumors and Manifestations

• Hemangioblastomas of the retina and central nervous system.
• Renal cysts that may progress to clear cell renal cell carcinoma.
• Pheochromocytomas.
• Endolymphatic sac tumors of the middle ear.
• Epididymal cysts or round ligament cysts.

Genetics

• Caused by mutations in the VHL gene.
  • The VHL gene mutation results in the loss of function of its protein product, pVHL.
  • Penetrance: 90% by the age of 65.
  • Mean age of diagnosis: 26 years.
• VHL gene mutations are also implicated in sporadic clear cell renal cell carcinoma, highlighting the role of VHL in renal cell carcinogenesis.

Molecular Mechanisms

• The VHL protein (pVHL): A tumor suppressor with a key role in the cell’s response to hypoxia.
  • Under normal conditions: pVHL targets the HIF-α subunits for oxygen-dependent proteolysis.
  • In the absence of pVHL:
    • HIF1α and HIF2α persist, leading to increased HIF transcriptional activity.
    • This results in upregulation of HIF target genes, including:
      • VEGF (vascular endothelial growth factor)
      • GLUT1 (glucose transporter 1)
      • Erythropoietin (involved in red blood cell production)
    • These actions occur independent of oxygen levels, promoting tumor growth and angiogenesis.
• Additional roles of pVHL:
  • Regulation of ECM (extracellular matrix) turnover.
  • Microtubule stability.

Clinical Significance

• Loss of VHL function is a critical event in the progression of renal cell carcinoma.
  • Experiments demonstrate that reintroducing wild-type VHL into VHL-deficient renal cancer cell lines suppresses tumor growth.

This summary provides an overview of von Hippel–Lindau syndrome, emphasizing its genetic basis, associated tumors, and the molecular role of pVHL in tumor suppression and hypoxia regulation.

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Cancer Epigenetics

Epigenetic Inheritance

• Defined as heritable cellular information other than nucleotide sequences that is passed down during cell division.
• Three main forms:
  1. DNA methylation
  2. Genomic imprinting
  3. Histone modification
• These epigenetic templates regulate gene expression and are transmitted to daughter cells independently of the DNA sequence.

1. DNA Methylation and Cancer

• DNA methylation at CpG dinucleotides is a well-studied epigenetic change.
• CpG islands:
  • Regions near gene promoters that are typically unmethylated in normal cells.
  • In cancer, CpG islands often become hypermethylated, leading to gene silencing.
• CpG island methylator phenotype:
  • Common in cancer, associated with silencing of tumor suppressor genes such as p16 and DNA mismatch repair genes like MLH1.
• IDH mutations:
  • Mutant IDH produces an oncometabolite that inhibits TET enzymes, leading to hypermethylation.
  • Results in tumor growth by preventing the CTCF protein from protecting genes from overactivation.
• Promoter methylation:
  • Leads to gene silencing, such as in MGMT, a DNA repair factor.
  • MGMT promoter hypermethylation has been observed in colorectal tumors, leading to increased DNA errors and cancer development.
• Hypomethylation and Cancer:
  • Hypomethylation leads to increased transcription of certain genes in tumors.
  • Example: Testicular germ cell tumors show genome-wide DNA hypomethylation.
    • Loss of methylation, particularly in pericentromeric satellite sequences, leads to chromosomal translocations.
    • Common in cancers of the ovary and breast.

2. Genomic Imprinting

• Genomic imprinting is the differential expression of parental alleles.
• In Wilms tumors:
  • Loss of imprinting leads to biallelic expression of IGF2.
  • Occurs along with hypermethylation of the H19 gene.
  • These epigenetic changes are among the earliest detectable genetic events in this cancer.

3. Histone Modification

• Histone modification (e.g., acetylation, methylation, phosphorylation) is key to chromatin compaction and gene regulation.
• Histone lysine demethylases (KDMs) play a role in cancer:
  • Example: H3K4 demethylases (KDM5 family) enable lung cancer and melanoma cell lines to evade anti-proliferative therapy by transitioning to a slow-cycling state.

Clinical Implications

• Epigenetic changes are a crucial aspect of cancer pathogenesis.
• Ongoing research is exploring epigenetic therapies that target these modifications, with many clinical trials underway.

This summary covers the key aspects of epigenetic regulation in cancer, including DNA methylation, hypomethylation, genomic imprinting, and histone modifications, and their roles in cancer development and potential therapeutic targets.

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Cancer Microbiome

Overview

• The role of the microbiome in cancer pathogenesis and treatment response has gained attention recently.
• Microbial pathogens are implicated in 15% to 20% of cancers.
• Dysbiosis (altered microbiome) is present in an even higher percentage of cancer patients.

Microbial Drivers of Tumorigenesis

• Helicobacter pylori is an example of a microbial pathogen linked to cancer (discussed in the Carcinogenesis section).
• Dysbiosis in the gastrointestinal tract:
  • In colorectal cancer, there is:
    • Decreased abundance of beneficial bacteria like Bacteroidetes and Firmicutes species.
    • Overrepresentation of potentially harmful bacteria like Fusobacterium.

Gut Microbiome and Tumor Immunity

• The gut microbiome plays a crucial role in the immune system, including tumor immunity.
• Mechanisms of microbiome involvement:
  1. Microbial byproducts:
     • Example: Butyrate produced by microbes can induce regulatory T cells.
  2. Disruption of gut barrier function:
     • Leads to altered mucosal immunity and potential immune dysregulation.

Impact on Cancer Treatment

• Intratumoral bacteria:
  • Example: Gammaproteobacteria found in pancreatic cancer metabolizes gemcitabine (a chemotherapy drug), converting it to an inactive form, reducing treatment efficacy.
• Microbiota and immunotherapy:
  • Emerging evidence suggests that altered microbiota can negatively impact the efficacy of immunotherapeutics used in cancer treatment.

This summary highlights the role of the microbiome in cancer development and its influence on tumor immunity and treatment responses, with examples of microbial contributions to tumorigenesis and chemotherapy resistance.

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Carcinogens

Definition

• A carcinogen is any agent that can contribute to tumor formation.
• Carcinogens can be:
  • Chemical
  • Physical
  • Biologic

Classification by the International Agency for Research on Cancer (IARC)

• The IARC maintains a comprehensive registry of human carcinogens, categorized based on evidence from epidemiological studies, animal models, and mutagenesis tests.

IARC Classification Groups

1. Group 1: Proven human carcinogens.
   • 120 agents in this group.
   • These agents have strong evidence of causing cancer in humans.
2. Group 2A: Probable human carcinogens.
   • 82 agents in this group.
   • Limited evidence of carcinogenicity in humans, but sufficient evidence in experimental animals.
3. Group 2B: Possible human carcinogens.
   • 311 agents in this group.
   • Limited evidence in humans and less than sufficient evidence in animal studies.
4. Group 3: Agents with inadequate evidence of carcinogenicity in both humans and experimental animals.
   • 499 agents in this group.
5. Group 4: Agents probably not carcinogenic to humans.
   • Only 1 agent in this category.

Accessing the IARC Registry

• The IARC registry of human carcinogens can be accessed online at www.iarc.fr.

Protein Tumor Markers

1. Carcinoembryonic Antigen (CEA)

• Used in: Colorectal cancer.
• Characteristics:
  • Oncofetal protein present in low concentrations in healthy adults.
  • Glycoprotein (200 kDa) located on the luminal side of epithelial intestinal cells.
  • Involved in cell adhesion and inhibits apoptosis related to ECM detachment.
• Testing:
  • Normal range: < 2.5 ng/mL (non-smokers), 2.5-5.0 ng/mL (borderline), > 5.0 ng/mL (elevated).
  • Smokers have a higher normal range (up to 5 ng/mL).
• Uses:
  • Screening: Not useful due to low sensitivity (5%-40% in localized disease).
  • Prognosis: Correlates with tumor burden; higher preoperative levels predict poorer survival.
  • Monitoring:
    • Used to monitor for recurrence.
    • A level > 5 ng/mL suggests recurrence (sensitivity 71%, specificity 88%).
    • For chemotherapy response, decreasing CEA levels correlate with improved survival in metastatic colorectal cancer.

2. α-Fetoprotein (AFP)

• Used in: Hepatocellular carcinoma (HCC) and nonseminomatous testicular cancer.
• Characteristics:
  • Oncofetal antigen synthesized by hepatocytes and gastrointestinal tissues.
• Testing:
  • Normal range: < 10 ng/mL.
  • Sensitivity for detecting HCC at 20 ng/mL: 54%.
• Uses:
  • Screening: Combined with ultrasound in high-risk populations, with variable cutoffs (15-200 ng/mL).
  • Prognosis: Correlates with tumor size and stage; levels > 400 ng/mL indicate poor prognosis.
  • Monitoring: Declines after successful treatment; levels < 10 ng/mL post-resection are ideal.

3. Carbohydrate Antigen 19-9 (CA 19-9)

• Used in: Pancreatic ductal adenocarcinoma.
• Characteristics:
  • Mucin-type glycoprotein expressed on pancreatic cancer cells.
• Testing:
  • Normal range: < 37 U/mL.
  • Not useful in patients with negative Lewis A antigen (10% of population).
• Uses:
  • Screening: Poor as a screening tool (sensitivity 79%-80%, specificity 82%-90% in symptomatic patients).
  • Prognosis: Higher levels correlate with advanced tumor stages.
  • Monitoring: Used to monitor treatment response and detect recurrence.

4. Prostate-Specific Antigen (PSA)

• Used in: Prostate cancer.
• Characteristics:
  • Serine protease involved in semen liquefaction.
• Testing:
  • Normal range:
    • Varies with age: 2.5 ng/mL (40-49 years), 3.5 ng/mL (50-59 years), 4.5 ng/mL (60-69 years), 6.5 ng/mL (>70 years).
    • PSA velocity > 0.75 ng/mL/year is considered abnormal.
    • Free-to-total PSA ratio < 10% improves diagnostic specificity.
• Uses:
  • Screening: Widely used for early detection, but its benefit is controversial.
  • Prognosis: Levels should normalize post-resection. Elevated levels after surgery indicate recurrence.
  • Monitoring: Used to track disease progression and response to therapy.

5. Carbohydrate Antigen 125 (CA 125)

• Used in: Ovarian cancer.
• Characteristics:
  • Carbohydrate epitope found on glycoproteins in various tissues.
• Testing:
  • Normal range: < 35 U/mL.
  • Elevated in 50% of early-stage and 80% of late-stage ovarian cancer patients.
• Uses:
  • Screening: Not effective as a screening tool due to poor specificity.
  • Prognosis: Elevated levels at diagnosis predict worse outcomes.
  • Monitoring: Levels correlate with treatment response and can predict recurrence.

6. α-Fetoprotein and Human Chorionic Gonadotropin in Testicular Germ Cell Tumors

• Used in: Nonseminomatous testicular cancers.
• Characteristics:
  • Human chorionic gonadotropin (hCG) is detected in 90% of choriocarcinomas.
  • AFP is expressed in:
    • 90%-95% of yolk sac tumors.
    • 20% of teratomas.
    • 10% of embryonal carcinomas.

This summary outlines key protein tumor markers, their uses, and the cancers they are associated with, emphasizing their roles in screening, prognosis, and monitoring treatment response.