Low-grade fibromyxoid sarcoma. A report of 12 cases.

Twelve cases of low-grade fibromyxoid sarcoma are presented. The patients' ages ranged from 6 to 51 years; all but three were between 26 and 46 years of age. The tumor was located in the thigh or inguinal area in four patients, in the shoulder area in three patients, and in the axilla-chest wall area, the perineum, the small bowel mesentery, the neck, and the buttock in one patient each. Tumor size (maximum dimension) varied from 3.5 to 15 cm in the nine cases in which it was known (median, 9.5 cm). Histologically, the neoplasms demonstrated contrasting fibrous and myxoid areas, a swirling, whorled growth pattern (at least in part), and bland, deceptively benign-appearing fibroblastic spindle cells; cellularity was low to moderate, mitotic figures were uncommon, and nuclear pleomorphism was usually absent or slight. Focal histologic findings in a minority of the cases included increased perivascular cellularity, moderate nuclear pleomorphism (more often in recurrent tumors), and, in myxoid areas, a rich capillary vascular network (vascularity was usually not prominent). On follow-up, nine patients experienced local recurrence (from one to numerous times); recurrence was subsequently controlled in five cases but not in the remaining four. Distant metastasis occurred in seven cases, chiefly to the lungs, but two of these patients were rendered tumor-free (to latest follow-up) by excision of metastases. At latest follow-up, four patients had died of tumor at 8, 9, 31, and 31 1/2 years, respectively, three were alive with recurrent or metastatic tumor at 6 1/2, 12 1/2, and 50 years, respectively, and five were alive and tumor-free at 5 1/2, 10 1/2, 12, 22 1/2, and 44 years, respectively. One tumor, in the patient who died at 31 years, demonstrated "dedifferentiation" at 30 years. Low-grade fibromyxoid sarcoma is a distinctive, indolent soft-tissue sarcoma.