Fibrosarcoma-malignant fibrous histiocytoma of the breast. A clinicopathological study of 32 cases.

We report the clinical and pathologic features of 32 sarcomas of the breast with features spanning the spectrum of fibrosarcomas-malignant fibrous histiocytomas. Neoplasms were categorized as high- or low-grade lesions depending on a combination of the degrees of atypia and mitotic activity. The majority of high-grade lesions had marked (3+) nuclear atypia and at least five mitotic figures per 10 hpf. High-grade lesions with moderate (2+) nuclear atypia had a mitotic activity of six or more mitotic figures per 10 hpf. All low-grade lesions had five or fewer mitotic figures per 10 hpf, and none had a score of the nuclear grade times mitotic figures of more than 10. The average mitotic activity in low-grade lesions was two mitotic figures per 10 hpf; the high-grade lesions had 12 mitotic figures per 10 hpf. Sixty-nine percent of the low-grade fibrosarcomas-malignant fibrous histiocytomas showed mild (1+) cytologic atypia, and 69% of the high-grade lesions showed severe (3+) cytologic atypia. The herringbone pattern was associated with a more favorable prognosis than the malignant fibrous histiocytoma pattern. Compared to the high-grade lesions, low-grade fibrosarcomas-malignant fibrous histiocytomas were slow-growing, produced fewer recurrences, and did not metastasize. Of the 16 women with low-grade lesions, all were free of tumor at last contact, despite recurrence in more than half of the patients. In contrast, 31% of the patients with high-grade lesions died of tumor, and 13% were alive with disease. Twenty-five percent of women with high-grade lesions developed distant metastases.