Metaplastic carcinoma of the breast is a relatively rare cancer and includes various histologic types. In this cancer, metaplastic elements are heterogeneous and sometimes mixed. We investigated, by histopathologic means, these elements and clinical implications that could indicate the clinical course (including the prognosis). Fifty-three metaplastic breast carcinoma cases and their prognoses were investigated by initially examining the presence or absence of spindle-cell elements, and then the presence or absence of other elements. Spindle cells were classified as high or low grade. The number of spindle-cell-positive cases was 24 (45%) of 53. The 24 spindle-cell (+) cases were subdivided into 12 high-grade (HGsp) (distant metastatic rate per 100 person-years, 13.27) and 12 low-grade (LGsp) (0.00) patients. Spindle-cell (-) cases were subdivided into 22 pure squamous cell carcinomas (5.93) and 7 matrix-producing carcinomas (0.00). There were significant differences among the 4 groups with regard to the disease-free period (P = .0081, log-rank test). The distant metastatic risks in the HGsp and pure squamous cell carcinomas groups were significantly higher than that in the matrix-producing carcinoma + LGsp group (nonmetastatic groups) after controlling for the effects of tumor size and lymph node metastasis (P = .019 and P = .016, respectively, Poisson regression model). The presence of high-grade spindle cells was related to the prognosis, and some histologic subtypes may be important with respect to the prognosis. The presence of high-grade spindle cells in metaplastic breast carcinoma may indicate aggressive behavior.
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