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Fibrolamellar Carcinoma (FLC)

Overview

  • Distinct from HCC: Originally considered part of the HCC spectrum, now classified as a separate entity due to distinct clinical, pathologic, and imaging features.
  • Demographics:
    • Affects young adults (average age: 25 years).
    • Occurs in absence of cirrhosis or traditional liver disease risk factors.
    • Equal prevalence in males and females.

Clinical and Pathological Features

  • Presentation:
    • Typically a large, solitary, well-demarcated mass (average diameter > 11 cm).
    • Central scar seen in 46-73% of cases.
    • Metastasis: Common at presentation, especially in the abdomen and chest, with prominent adenopathy.
  • Histology:
    • Bands of collagen organized in a lamellar pattern.
    • Tumor cells: Larger than normal hepatocytes, with granular, eosinophilic cytoplasm and prominent nucleoli.
    • Bile pigment and occasional fat or glycogen accumulation present.
    • Characteristic features include CK7 and CD68 positivity.

Genetics and Molecular Findings

  • Genetic abnormalities:
    • DNAJB1-PRKACA fusion resulting from a deletion on chromosome 19.
    • Overexpression of neuroendocrine genes (e.g., neurotensin, prohormone convertase 1).
    • Presence of chimeric protein coupling DNAJB1 with the catalytic domain of protein kinase A.

Imaging Characteristics

  • Ultrasound (US): Variable appearance, may show calcifications and a central hyperechoic scar.
  • CT Scan:
    • Unenhanced CT: Large, hypoattenuating, well-defined mass with a central scar.
    • Calcifications present in 43-64% of cases.
  • MRI:
    • T1-weighted: Typically low signal.
    • T2-weighted: Typically high signal, but the central scar often shows low signal due to fibrosis.
    • FLC tends to show more heterogeneous enhancement compared to FNH.

Diagnosis and Differentiation

  • Differential diagnosis: Often confused with FNH or conventional HCC due to overlapping imaging features.
  • Key differentiators:
    • Calcifications and low T2 signal in central scar favor FLC over FNH.
    • Enhanced scarring on delayed phases and variability in enhancement are typical for FLC.

Treatment and Prognosis

  • Resection:
    • Offers the best chance of long-term survival.
    • 5-year survival rate: 59% after resection, compared to 40% for conventional HCC.
  • Chemotherapy: Generally ineffective.
  • Prognosis: Better than standard HCC, with slow-growing tumors often resectable despite extrahepatic recurrences.