Primitive Nonneural Granular Cell Tumor (So-called Atypical Polypoid Granular Cell Tumor). Report of 2 Cases With Immunohistochemical and Ultrastructural Correlation

Primitive nonneural granular cell tumors (so-called atypical cutaneous granular cell tumors) were first described in 1991, followed by few case reports, and 2 recent larger series. We report here 2 additional cases in 2 women aged 73 and 74, who presented with 0.6- and 0.4-cm skin nodules on the right side of the jaw and the forearm, respectively. Biopsies showed cutaneous granular cell neoplasms with epithelioid morphology. The cells exhibited nuclear pleomorphism and brisk mitotic activity with atypical mitoses. Immunohistochemically, the tumor cells expressed vimentin and PGP 9.5 but lacked S-100 and CD34 expression. Ultrastructurally, both cases showed primitive cells packed with large secondary lysosomes. Primitive nonneural granular cell tumors seem to consist of neoplastic proliferating cells that fail to break down uncharacterized cellular material within the lysosomes. They are, however, different from classic granular cell tumor by lacking neural differentiation. Despite reported worrisome cellular atypia, these rare tumors seem to pursue a favorable outcome.