Twenty‐six cases of breast carcinoma demonstrating pseudosarcomatous metaplasia are described, and their clinical and pathologic aspects are correlated. The metaplastic elements include mature and immature bone, cartilage, myxoid stroma, loose fibromyxoid and dense spindle‐cell stroma, and anaplastic stroma with giant cell features. Light and electron microscopic examination demonstrated an orderly sequence of transformation and dedifferentiation of epithelial cells to become undifferentiated mesenchymal cells. These tumors are more aggressive than purely epithelial carcinomas. The overall survival rate was 44%. Five‐year survival figures for TNM Stages I, II, and III lesions were 56%, 26%, and 18%, respectively. The incidence of lymph node metastasis was 25% despite the large size of many of these tumors. Systemic metastases replicated the range of metaplastic elements seen in the primary site. Patients with tumors composed predominantly of pseudosarcomatous elements had worse prognoses than those with predominantly epithelial components (28% versus 62%, 5‐year survival).

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Four vulvectomy specimens from patients with vulvar Paget's disease were studied by means of subserial total sectioning. In each case, the extent of histologically demonstrable disease was far greater than that of the visible lesion, the outline of the involved area was highly irregular, and multiple foci of disease were present. The implications of the findings for treatment selection, intraoperative management, and histogenesis are discussed.