Microscopic description and IHC:
This is a 3.0 x 2.9 x 2.1 cm mass that appeared firm, white, and well circumscribed on gross examination. Histologically, it consists of mostly epithelioid cells with focal spindled areas, arranged around vascular channels, with significant (>50%) stromal hyalinization/sclerosis. It is diffusely positive for SMA and Desmin (as opposed to a conventional PEComa, which is usually only focally desmin positive), as well as diffusely positive for MITF-1 and focally positive for HMB45, both of which are melanocyte markers.
Discussion:
The sclerosing PEComa is a newly described variant of PEComas, which are mesenchymal tumors consisting of perivascular epithelioid cells, of which a non-neoplastic cell component has yet to be identified. They classically express both smooth muscle and melanocyte markers. As one could have guessed, this particular entity has a prominent sclerotic component (at least 50% sclerotic, to be exact). It has a predilection for the retroperitoneum, particularly the pararenal region, and shows extensive stromal hyalinization on Hematoxylin and Eosin stain (H&E). They are seen almost exclusively in women. Additionally, the sclerosing PEComa is much less associated with tuberous sclerosis. Although they tend to follow an indolent course, there have been case reports of malignant sclerosing PEComas.
References:
G. Abhirup B, Kaushal K, Sanket M, et al. Malignant hepatic perivascular epithelioid cell tumor (PEComa) – case report and a brief review. Journal of the Egyptian National Cancer Institute. 2015;27:239–242.
J. Zhao Y, Bui MM, Spiess PE, et al. Sclerosing PEComa of the kidney: clinicopathologic analysis of 2 cases and review of the literature. Clinical Genitourinary Cancer. 2014;12, 5:e229-32.