Intracytoplasmic inclusions (including the so-called "rhabdoid" phenotype) in pancreatic endocrine tumors

The cytoplasm of pancreatic endocrine tumors (PET) can show a diverse range of appearances from clear, to oncocytic, to intracellular mucin accumulation, and the presence of intracytoplasmic inclusions. Intracytoplasmic eosinophilic inclusions can vary morphologically and the spectrum ranges from small, dot-like hyaline inclusions, to deeply acidophilic/eosinophilic ones that occupy almost the whole cytoplasm and displace the nucleus eccentrically: the so-called "rhabdoid" phenotype. The aim of this study was to analyze the frequency, morphology, behavior, and relationship to clinicopathological features of large intracytoplasmic inclusions, including the rhabdoid phenotype, in a large number of PET. The morphological features of 84 cases were assessed for the presence of large, globular intracytoplasmic inclusions. Fourteen of 84 cases contained intracytoplasmic inclusions with 5 cases containing cells conforming to the characteristic rhabdoid morphology. The remaining nine cases showed pale intracytoplasmic inclusions. Four of the five cases with rhabdoid cells had spread to lymph nodes and/or peripancreatic fatty tissue. This study confirms that a spectrum of large intracytoplasmic inclusions is encountered in PET, ranging from lightly eosinophilic intracytoplasmic globules to the more typical rhabdoid phenotype (deeply eosinophilic inclusions). This phenotype, in particular the rhabdoid cells, is worthy of attention as a proportion may show lymphovascular invasion with evidence of metastasis at the time of presentation, irrespective of size, mitotic rates, or necrosis.