Retroperitoneal pararenal dedifferentiated liposarcoma with epithelioid/neuroendocrine features, somatostatin-positive.

We have read with interest the article entitled ‘Gastrointestinal Neuroendocrine Tumours: A Single-Centre Experience’, published in Forum of Clinical Oncology^[1].

We would like to point out, however, that not all intra-abdominal lesions with neuroendocrine phenotypic expression are gastro-entero-hepato-pancreatic neuroendocrine epithelial neoplasms.

We present the case of a woman in her sixties with a pararenal mass 12 cm in diameter, radiologically doubtful as to being of renal origin or from the pancreatic tail: surgery revealed that this mass was extra-renal and extra-pancreatic, thus sparing both organs.

Histology showed an epithelioid nested neoplasia, with necrosis and several mitoses (Fig. 1A); notably, spindle cell and adipocytic areas with cytological atypia are observed on the surrounding border (Fig. 1B). Immunohistochemistry results were the following: cytokeratins−; chromogranin−; synaptophysin−; NSE+ (Fig. 1C); CD56+; somatostatin+ (Fig. 1D); insulin−; glucagon−; gastrin−; serotonin−; pancreatic polypeptide−; pS100−; SOX10−; melan A−; HMB45−; vimentin−/+; CD31−; CD34−; FLI1−; desmin−; smooth muscle actin −/+; muscle specific actin−; CD117−; DOG1−; inhibin−; MUC1−; tyrosinase−; GATA3−; CD99−; BCL2+; WT1−.

Figure 1:

The findings led us to a malignant neoplasm with neuroendocrine expression (NSE, somatostatin, CD56), whose true nature was, however, difficult to define: the epithelioid morphology found does not allow us to define an epithelial origin; furthermore, neuroendocrine tumours are cytokeratin-negative only rarely.

The following were considered in the differential diagnosis: pancreatic or gastro-enteric neuroendocrine tumour, paraganglioma, adrenal carcinoma, GIST, PEComa, schwannoma^[2], and melanoma, but they are excluded by immunohistochemistry results.

The positivities for vimentin and actin, although in rare neoplastic elements, led to the suspicion of a mesenchymal nature, and the atypical features in the surrounding fibroadipose tissue reinforced this hypothesis: we therefore proceeded with the assessment of MDM2 gene amplification by FISH. The result was: amplified (Fig. 2).

Figure 2:

Pararenal malignancies may originate from the renal capsule or the adrenal gland^[3,4]; however, more frequently, they arise from the retroperitoneal soft tissues: the most frequent is liposarcoma. Such a neoplasm derives from adipocytes but can dedifferentiate to many histological lines: the epithelioid/neuroendocrine is one of the rarest^[5]. In any case, the vast majority of liposarcomas, even dedifferentiated ones, show amplification of the MDM2 gene.

It is therefore thanks to the above FISH result that it was possible to label this lesion as a liposarcoma, although exceptionally rare in this form of epithelioid/neuroendocrine dedifferentiation with somatostatin expression^[6].