Metastatic Pleomorphic Dermal Sarcoma Involving Tonsil and Thyroid: An Unusual Presentation

Pleomorphic dermal sarcoma (PDS) is a rare dermal-based mesenchymal tumor that shares histologic characteristics with atypical fibroxanthoma (AFX), but demonstrates aggressive features increasing the risk of local recurrence or metastases. We report a unique case of a 62-year-old man with a recent history of left-groin PDS, now with a 2-cm pedunculated left tonsillar mass and two hypermetabolic nodules in the left thyroid. Microscopically, the tonsillar biopsy demonstrated infiltrating spindle cell neoplasm composed of highly pleomorphic tumor cells with abundant mitoses. The left hemithyroidectomy specimen also demonstrated similar pleomorphic spindled tumor cells infiltrating thyroid parenchyma with perineural invasion and focal osseous and chondroid components. Immunohistochemically, both tumors were diffusely positive for smooth muscle actin. Focal nonspecific positive staining with p53, SATB2, and S100 was observed in the thyroid tumor. Additional markers, including p40, CK5, p63, pancytokeratin, CAM5.2, S100, SOX10, Melan-A, HMB45, CD45, CD68, CD163, caldesmon, p16, TTF1, PAX8, and calcitonin, were all negative. INI-1 expression was retained. Molecular analysis showed that the tumor harbored PDGFRA deletion of exon 9 and amplification, PTCH1 A300fs*24, MDM2 amplification, CDKN2A/B loss, and FRS2 amplification. Compared with the patient’s groin tumor, the current tumors showed similar morphology. Overall, the histologic and immunohistochemical findings are consistent with metastatic PDS to the tonsil and thyroid. Although PDS is commonly found on the sun-exposed skin in the elderly, this case highlights an unusual primary site as well as peculiar locations for the metastasis of PDS. Treatment and management of the patient are also considered.