DNAJB1-PRKACA is specific for fibrolamellar carcinoma

Abstract

Fibrolamellar carcinoma is a distinct subtype of hepatocellular carcinoma that predominantly affects young patients without underlying cirrhosis. A recurrent DNAJB1-PRKACA fusion has recently been reported in fibrolamellar carcinomas. To determine the specificity of this fusion and to develop routinely available clinical methods of detection, we developed an RT-PCR assay for paraffin-embedded tissues and a FISH probe for detection of the rearrangements of the PRKACA locus. We also developed an RNA in situ hybridization assay to assess expression levels of the total chimeric transcript and wild-type transcripts. A total of 106 primary liver tumors were studied by RT-PCR, including 26 fibrolamellar carcinomas (4 of which were metastases to the abdominal wall or lymph nodes), 25 conventional hepatocellular carcinomas, 25 cholangiocarcinomas, 25 hepatic adenomas, and 5 hepatoblastomas. RT-PCR was successful in 92% of tested fibrolamellar carcinoma cases (24/26) and the DNAJB1-PRKACA fusion transcript was found in all fibrolamellar carcinomas but not in other tumor types. FISH was tested in 19 fibrolamellar carcinomas and in 6 scirrhous hepatocellular carcinomas, which can closely mimic fibrolamellar carcinoma. Rearrangements of the PRKACA locus was seen in all 19 fibrolamellar carcinoma specimens, but in none of the scirrhous hepatocellular carcinomas. Finally, a RNA in situ hybridization strategy was positive in 7/7 successfully hybridized cases, and showed mRNA over-expression in all of the fibrolamellar carcinomas. In addition, the stromal cells embedded in the characteristic intratumoral fibrosis of fibrolamellar carcinomas and the background liver tissues were negative for the DNAJB1-PRKACA fusion by all tested methods. In conclusion, detection of DNAJB1-PRKACA is a very sensitive and specific finding in support of the diagnosis of fibrolamellar carcinoma.

Hepatic adenomas with synchronous or metachronous fibrolamellar carcinomas: both are characterized by LFABP loss

“…11 An alternative method is detection of recurrent somatic DNAJB1-PRKACA in fibrolamellar carcinoma. 1 Although rare, cases of hepatic adenomas can develop in livers with synchronous or metachronous fibrolamellar carcinomas. This is the first series of Hepatic adenomas and fibrolamellar carcinoma such cases and shows several key findings.…”

“…PRKACA FISH used the validated probe and methodology as described previously. 1 FISH slides were visualized and scored by two experienced technologists who each independently evaluated 50 tumor nuclei.…”

“…The consistent loss of LFABP was not anticipated in the fibrolamellar carcinomas that co-occurred with or followed resection for hepatic adenomas, so we studied LFABP expression in a second cohort of 19 fibrolamellar carcinomas, including 11 previously published tumors 1 and an additional new set of 8 tumors. The diagnosis in the additional set of eight fibrolamellar carcinomas was first confirmed at the genomic level by detection of the PRKACA rearrangement by interphase FISH: all were positive.…”

“…The carcinoma is histologically distinct and shows a consistent somatic deletion leading to DNAJB1-PRKACA fusion transcripts. 1,2 Although the tumorigenic mechanism for this fusion protein is not yet proven, the fusion protein appears to drive overexpression of PRKACA. PRKACA is one of the catalytic subunits of protein kinase A, a key regulatory kinase with numerous downstream signaling targets.…”

Environmental exposures as a risk factor for fibrolamellar carcinoma

“…8 At the molecular level, fibrolamellar carcinomas show a specific DNAJB1-PRKACA fusion transcript in almost all bona fide cases. 7,9 The etiological risk factors for fibrolamellar carcinomas are unknown, as they arise in livers without underlying liver disease and without fibrosis. However, as one possible clue, Craig and Edmonson noted that no cases of fibrolamellar carcinoma were identified in large autopsy studies 10,11 or in the consultation practice of Dr Edmonson before World War II (1939)(1940)(1941)(1942)(1943)(1944)(1945).…”