Hepatocellular carcinoma (HCC) is the sixth most common cancer worldwide and the fourth major cause of cancer-related death. Conventional HCC typically presents in individuals in their fifties and sixties with underlying chronic liver disease or cirrhosis caused by hepatitis B or C virus infection, alcohol intake, or metabolic syndromes. However, HCC remains the most common liver malignancy in children and young adults. Conventional HCC usually harbor TP53 and β-catenin (CTNNB1) mutations. Edmondson, in 1956, first described Fibrolamellar carcinoma (FLC), a rare and unique primary hepatocellular malignancy (2). Fibrolamellar carcinoma typically arises from the noncirrhotic liver. Fibrolamellar carcinoma affects mostly late adolescents and young adults. Approximately 80% of FLCs occur in individuals aged between 10 and 40 years, with an average age of presentation of 25 years. Men and women are affected equally (3). The most common manifestation of FLC is an abdominal mass. FLCs demonstrate activation of protein kinase A, most commonly through a DNAJB1-PRKACA fusion, secondary to intrachromosomal deletion on chromosome 19. FLCs frequently present late recurrences with a 5-year recurrence-free survival of up to 50%. We are presenting a case of a 16-year-old female with abdominal mass, hepatomegaly, and multiple lung masses concerning metastasis. This paper emphasizes the clinical presentation, the characteristic gross and microscopic findings, molecular pathology prognosis, and unique characteristics that differentiate fibrolamellar carcinoma from other variants of HCC.

Our patient is a 16-year-old female who presented with abdominal pain for the past 8 months. She had a fever and an unintentional seven lb. weight loss. She also had tonsillar exudates, cervical lymphadenopathy, and hepatomegaly. Her monospot test was positive. CT abdomen with IV contrast shows a large (13 cm) heterogeneous appearing, highly vascular nodular right hepatic mass (Figure 1). The mass appears expansile/exophytic, and is associated with hepatomegaly. Additional smaller nodular masses were noted in liver segments 4,7, 8, and porta hepatis, which encircle the portal vein. CT chest with IV contrast reveals three distinct soft tissue nodules in the lungs concerning distant metastases of known liver mass. CA 19-9 was elevated; alpha-fetoprotein and CEA are normal. Subsequently, an IR biopsy was performed.

On pathological examination, the tumor is composed of large and polygonal cells with well-defined cell borders, abundant granular eosinophilic cytoplasm, and moderate nuclear atypia with prominent macro nucleoli. The neoplastic cells are arranged in cords and pseudo acinar formation (small nests) around the canaliculi separated by dense acellular collagenized stroma. Pale hyaline bodies are also seen. The fibrous bands merge into a central scar. CK-7 was solid and diffuse positive, PASD highlighted the hyaline bodies, trichrome showed collagen bundles, and reticulum showed abnormal architecture. CD34 performed was negative. Histopathology and immunohistochemistry favored fibrolamellar hepatocellular carcinoma (FLC) (Figure 2). The specimen was sent for fluorescence in situ hybridization (FISH) molecular analysis. FISH results showed a molecular rearrangement involving the PRKACA gene region (19p13.20) with loss of the 5’PRAKACA probe and retention of the 3’ PRKACA probe. This signal pattern has been correlated with the DNAJB1-PRKACA fusion event and clinically associated with fibrolamellar carcinoma (4). A diagnosis of fibrolamellar carcinoma is made. The patient is scheduled for chemotherapeutic management followed by surgical resection.

In the 5th edition of WHO classification of the tumors of the digestive system, in addition to the conventional HCC, the WHO recognized eight morphological subtypes of HCC: Fibrolamellar HCC, Scirrhous HCC, clear cell type HCC, steatohepatitis type HCC, Macro trabecular massive HCC, Chromophobe HCC, Neutrophil rich HCC, and Lymphocyte rich HCC.

Fibrolamellar carcinoma is mainly seen in young adults. It is rarely seen in patients aged above 50 years. The most common clinical finding is abdominal pain or a palpable mass. Other gastrointestinal symptoms are abdominal distention from ascites, gynecomastia due to associated high levels of aromatase expression, rarely altered mental status secondary to hyperammonemia, and acquired ornithine transcarboxylase deficiency. This can metastasize to the lymph nodes, peritoneum, lung, and in rare cases brain. Serum levels of aspartate aminotransferase and alanine aminotransferase can be normal or mildly elevated. Alpha-fetoprotein (AFP) levels are normal, although approximately 10% of reported cases have had AFP elevations in the 200 ng/mL range or greater (5). More than 50% of the patients affected by Fibrolamellar carcinoma are Caucasian, while greater than 80% of patients with conventional HCC are Caucasian (6). Cirrhotic liver morphology is seen in less than 10% of patients diagnosed with Fibrolamellar carcinoma (7).

Imaging studies usually show a solitary mass with well-defined margins with decreased attenuation. The mass demonstrates increased contrast avidity in the arterial phase, reflecting these tumors’ high blood supply. Most of the patients exhibit a calcified central scar which shows contrast avidity in this later phase. Focal nodular hyperplasia, Giant cavernous hemangioma, and HCC are the differential diagnoses based on radiological findings.

Fibrolamellar carcinoma forms a multinodular, large, and tan-colored mass with a green hue due to bile production by the neoplastic cells. A central scar is noted in most cases, often calcified (9, 10). The adjacent nonneoplastic liver is noncirrhotic. Fibrolamellar carcinoma shows nests and sheets of large polygonal tumor cells with vesicular nuclei and single prominent nucleoli. They present with abundant granular eosinophilic cytoplasm and have fibrous stroma composed of collagen. Pale hyaline bodies are identified more frequently than in conventional HCC.

Fibrolamellar carcinoma expresses markers of hepatocellular differentiation like HepPar1 and Arginase. Keratin 7 and CD68 are helpful affirmative markers for FLC diagnosis in 85 to 90% of cases (11). CK19, fibrinogen (pale bodies), alpha-1 antitrypsin, polyclonal CEA, and CAM 5.2 (CK8 / 18) are other immunohistochemical markers that show positive expression in fibrolamellar carcinoma. Liver fatty acid-binding protein (LFABP) shows negative expression in tumor cells similar to conventional HCC.

DNAjb1 gene encodes DnaJ or Hsp 40 (heat shock protein 40 kD) protein that stimulates the ATPase activity of Hsp70 heat-shock proteins to promote protein folding and prevent misfolded protein aggregation. PRKACA gene encodes one of the catalytic subunits of protein kinase A (12). Honeyman et al. discovered a novel somatic 400 kb deletion on the short arm of chromosome 19, giving rise to DNAJB1–PRKACA gene fusion protein. The chimeric protein product of the DNAJB1-PRKACA fusion connects exon 1 of DNAJB1 to exons 2–10 of PRKACA, maintaining the N-terminal of the DnaJ heat-shock protein and the kinase domain of PRKACA functional. This chimeric fusion protein activates the kinase activity of PRKACA catalytic subunit alpha and functions as the oncogenic driver of fibrolamellar carcinoma (13). Conventional cytogenetic techniques initially failed to identify this 400 kbp deletion and were later discovered using RNA sequencing in 2014. DNAJB1-PRKACA fusions are identified by targeted RNA fusion panel sequencing or by PRKACA break apart fluorescent in situ hybridization. FISH-based testing is highly specific for FLC (11). DNAJB1-PRKACA chimeric fusion protein has also been reported in tumors of pancreaticobiliary origin, questioning the relation of fibrolamellar carcinoma to other gastrointestinal tumors (14) (Figure 3). Recently, a clinical test for fibrolamellar carcinoma was developed based on FISH to detect the PRKACA rearrangement and was positive in all 26 cases of fibrolamellar carcinoma and none of the conventional HCCs. Rare cases are characterized by biallelic PRKAR1A loss (primarily in patients with the Carney complex) instead of the above fusion gene (15). A single claim characterized by PRKACA amplification without genomic changes has been identified (9). Fibrolamellar carcinomas show fewer chromosomal abnormalities than those reported in conventional HCC literature (16).

The chief morphologic mimics of FLC are scirrhous HCC, conventional HCC, poorly differentiated cholangiocarcinoma, and metastatic pancreatic neuroendocrine tumors. Both HCC and the scirrhous variant of HCC arise in a background of cirrhosis and are characterized by serum AFP elevation (17). Scirrhous HCC may express CK7- and CK19-like FLC but may be negative for hepatocellular markers (18, 19). Both cholangiocarcinoma and FLC are associated with prominent fibrosis, but the cytomorphologic characteristics of FLC differ from cholangiocarcinoma (9). Mixed FLC is a unique and rare liver tumor defined by pure FLC and conventional hepatocellular components. It has a worse prognosis than its solitary counterparts. (20). Tumors with HCC and FLC histological features have been described as mixed FLC (Table 1). Mixed-FLC/HCC is frequently seen in older females, all above 35 years, and have a poor prognosis. Similar to FLC, Mixed FLC/HCC is seen in patients with no underlying liver cirrhosis. BAP-1 inactivating alterations are identified in mixed-FLC/HCC instead of DNAJB1-PRKACA fusion (21)

Ruptured FLC occurs rarely, and mortality in the acute phase is very high. However, after complete surgical resection, disease recurrence is high in the first 5 years. FLCs frequently present with late recurrences; 5-year recurrence-free survival is approximately 10 to 20%. Tumors > 5 cm in size are at high risk for a rupture with increased mortality and recurrence rates secondary to significant tumor spillage. While an emergency hepatectomy is preferred in unstable patients, hemodynamically stable patients can undergo radiologic transarterial embolization for hemostasis followed by staged hepatectomy (8). Vena cava obstruction has also been reported, but this is less common. FLC may uncommonly present with paraneoplastic manifestations. FLC often presents with regional lymph node metastases and spreads along the peritoneum. Ovarian metastases have been reported (9).

The most common site of FLC metastasis is the lung which is consistent with our case. In most HCC patients, distant metastases present as small solitary nodules. (11, 22). Even though surgery is the primary mode of treatment, only 30% of newly diagnosed patients undergo surgery, and the 5-year survival rate is less than 80% (23). Regardless of combination with neoadjuvant chemotherapy, surgery offers better survival than systemic therapy alone (24). Most inoperable HCC cases remain unresponsive to chemotherapy, with a poor prognosis (25).

Fibrolamellar carcinoma is emerging as a distinct entity on its own due to its origin from a structurally and functionally normal liver and its unique pathological and molecular characteristics. Even though imaging techniques like CT and MRI play a role in diagnosing FLC, a combination of histopathological examination and molecular characterization is critical for an accurate diagnosis.