Primary Hepatic Mixed Acinar-Neuroendocrine Tumor: A Rare Case of a Liver Mass

Abstract

Extra-pancreatic primary acinar cell carcinomas (ACC) are rare and have been reported in the stomach, jejunum, colon and liver. Of the seven hepatic cases reported, most presented with abdominal pain, a liver mass and no pancreatic involvement. This case is one among the unusual cases reported. A 67-year-old lady with past history of chronic hepatitis B infection presented with progressively worsening abdominal pain. Lab workup revealed an elevated lipase (3532 U/L), a normal liver function test, AFP and CA19-9. Abdominal ultrasound and CT showed an 11cm by 8cm heterogeneously enhancing mass in the right hepatic lobe with central enhancement [Figure 1] and no involvement of the pancreas or the biliary tree. Histopathology of the mass revealed atypical proliferation of neoplastic cells with pseudo-glandular formation and occasional prominent nucleoli [Figure 2a]. The cells stained positive for pancytokeratin, CK7, chromogranin, synaptophysin [Figure 2b] and trypsin; and negative for Hep-Par 1 [Figure 3], monoclonal CEA and CA19-9. The histologic features and immunophenotype were consistent with mixed acinar-neuroendocrine tumor. Surveillance MRI and endoscopic ultrasound (EUS) did not demonstrate a pancreatic mass leading to a diagnosis of primary hepatic ACC. It was determined that the tumor was not surgically resectable due to vascular proximity and the patient was referred to an oncologist for systemic chemotherapy. Patients with rare primary hepatic ACC usually present with abdominal pain with normal to low elevations of AFP and CA19-9. A para-neoplastic syndrome causing lipase hyper-secretion as seen in this patient has been mentioned in the literature. CT scan usually shows a single large hypo-enhancing lesion with areas of necrosis or multiple smaller solid lesions. Histopathology reveals typical tumor cells with immmuno-histochemistry demonstrating positivity for trypsin and chymotrypsin for acinar differentiation; synaptophysin for neuroendocrine differentiation. Multiple theories including presence of common progenitor cells showing aberrant pancreatic differentiation or occurrence of heterotopic or metaplastic pancreatic tissue among liver tissue has been implicated in the etio-pathogenesis. This case highlights the occurrence of a rare tumor and that it should be considered in the differential when a vascular tumor is detected in an otherwise healthy liver with normal tumor markers.2320_A Figure 1. shows axial and sagittal sections of Abdominal CT scan demonstrating the extent of the tumor2320_B Figure 2. (a) shows pseudo-glandular formation and prominent nucleoli on H and E stain and Figure 2 (b) shows tumor cells staining positive for synaptophysin2320_C Figure 3. Figure 3 shows islands of normal hepatic tissue with negative staining for Hep-Par 1