Abstract:

Dermatofibrosarcoma protuberans (DFSP) is a rare cutaneous malignancy, with classic DFSP having metastatic rates less than 1%. We report a patient with DFSP without fibrosarcomatous transformation having pulmonary metastasis 4 years after wide local excision. A 30-year-old male first noticed an enlarging left upper arm mass in 2009. MRI in 2017 demonstrated a 4.9 cm upper extremity skin tumor. Biopsy showed a biphasic CD34-positive, spindle cell neoplasm with hypercellular areas having a storiform pattern, entrapped adipocytes, 2 mitoses per 10 hpf and hyperchromatic nuclei alternating with hypocellular zones having spindle cells in a fibromucinous stroma with prominent capillaries. There was no necrosis or nuclear anaplasia. The patient was diagnosed with DFSP without fibrosarcomatous transformation and clear surgical margins were achieved after three excisions. Chest CT and PET scan four years later showed a 4.9 cm fluorodeoxyglucose-avid right lung mass. Right middle lobectomy revealed metastatic CD34-positive DFSP with 6 mitoses per 10 hpf, no anaplasia and no necrosis. PD-L1 staining was present in 50% of the cells in the metastastasis but was negative in the primary. The primary and the metastasis had very few CD8 positive and rare PD1 positive lymphocytes. While DFSP is typically locally aggressive but rarely metastatic, fibrosarcomatous transformation carries a 10-15% chance of metastasis. There are few reports of differential expression of PD-L1 in metastatic versus primary lesions of DFSP with fibrosarcomatous transformation. Our report is additional evidence of PD-L1 expression in metastatic DFSP and indicates PD-L1 staining may exist in the absence of fibrosarcomatous transformation.

Financial Disclosure:
No current or relevant financial relationships exist.

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Alison Hollis, BS