Medullary carcinoma of the breast. A multicenter study of its diagnostic consistency.

Nine pathologists from different institutions reviewed in a double-blind study 16 breast tumors previously indexed as typical medullary carcinoma, atypical medullary carcinoma, or infiltrative ductal carcinoma. A set of 16 slides was circulated two times among the nine pathologists. The diagnoses of typical and atypical medullary carcinomas were based on a definition given by Ridolfi et al. The interobserver and intraobserver agreement was low, with a kappa value of less than .50. The only histological criterion that had more than 50% agreement was the presence or absence of an in situ component in the tumor, assuming that the disagreement of one pathologist is accepted. This study is a snapshot of the problems encountered in the diagnosis of typical medullary carcinoma in a routine context and it shows high levels of variations in diagnostic consistency.