Infiltrating lobular carcinoma of the female breast. Deviations from the usual histopathologic appearance.

Twenty-two cases of breast tumor with infiltrating lobular carcinoma were studied. Thirteen showed the classic single-file pattern as a sole component, and 6 as a predominant pattern; the less common confluent pattern was found in 3 instances as a predominant component. Mucin secretion was evidenced in 59% of the primary tumors; it was a prominent feature in only 1 case. Nine tumors were associated with in situ lobular carcinoma. In 14, nodal metastases had occurred at the moment of diagnosis. In 50% of the metastases, intracellular mucin secretion was present. It appears that the diagnosis of infiltrating lobular carcinoma relies on the convergence of multiple histocytologic hallmarks, as much in the primary tumors as in the metastases. Deviations from the classic appearance need to be recognized as true lobular carcinomas, and even in these cases it is suggested that the well established term lobular carcinoma be maintained.