Metastasizing cellular dermatofibroma. A report of two cases.

Two cases of metastasizing cellular dermatofibroma (cutaneous fibrous histiocytoma) are presented. The first patient, an 18-year-old man, had a nodule excised from his right upper thigh. He developed three local recurrences at 1.5, 2, and 2.5 years and metastasis to inguinal lymph nodes. He underwent lung segmentectomies for metastases 1.5 and 4 years later and was alive with no evidence of tumor at latest follow-up, which was 15 months after the last surgery. The second patient, a 33-year-old man, had a nodule removed from his right posterior neck. The tumor recurred 3 months later and was reexcised. Right cervical lymph node metastases were excised at 7 and 8 years. A year later, a right cervical lymph node dissection yielded one positive node of 35, and multiple metastases were excised from the right lung. The patient was alive with lung metastases 6 years later, which was the latest follow-up. Grossly, both tumors were single 2 cm nonulcerated dermal-subcutaneous nodules. Histologically, they were characteristic of cellular dermatofibroma; they were composed of plump to spindled "fibrohistiocytic" cells arranged in a storiform pattern and had areas of hemorrhage, hemosiderin, and infiltration between dermal collagen bundles peripherally. Recurrences and metastases were histologically similar except that lung metastases were cystic. The alternative diagnosis of angiomatoid malignant fibrous histiocytoma was considered for these two cases but was excluded because the tumors were partly dermal, had a well-defined storiform pattern, and lacked large blood lakes, multinodularity, a fibrous pseudocapsule, and surrounding chronic inflammation. We conclude that dermatofibromas can rarely metastasize. Risk factors for metastasis may include relatively large size, high cellularity, and local recurrence. Judging from these two cases, metastasizing dermatofibromas behave in an indolent manner.