T-cell Clonality in Pleomorphic Dermal Sarcoma in Male Veterans: A Report of 2 Cases and a Review of the Literature.

Abstract: The standard treatment of choice for pleomorphic dermal sarcoma (PDS), a relatively uncommon soft tissue sarcoma and 1 morphologically similar to atypical fibroxanthoma, is wide local excision with close clinical follow-up. Studies regarding management of advanced/metastatic PDS with immune checkpoint inhibitors are limited as most STSs have historically been viewed as being immunologically inert. Contradicting this belief, in this report, we describe 2 cases of PDS with a robust host response. Histopathology of both cases revealed a dermal neoplasm comprising mitotically active, pleomorphic, spindled-to-ovoid cells, which were immunohistochemically negative for keratinocytic, melanocytic, and smooth muscle markers. An unusual feature in both cases was the presence of a brisk host response. Additional workup of the infiltrating lymphocyte population revealed an abnormal CD4:CD8 ratio in both cases, with the proportion of CD8 + lymphocytes surpassing (case 1) and equaling (case 2) that of the CD4 + T-lymphocyte population. The increased proportion of CD8 + lymphocytes prompted the additional workup of TCR gene rearrangement, which revealed a clonal population of T lymphocytes in both cases. The robust and clonal T-lymphocyte host response in both of our cases suggests that PDS appears to fit the classic model of an inflammatory-type tumor and may be a candidate for checkpoint inhibition. Future work includes additional reports of cases of PDS with an infiltrating clonal T-lymphocyte population and detailing the function and specificity of the infiltrating T lymphocytes to ascertain whether they have the potential to recognize and lyse the tumors they colonize.