Histologic variants of infiltrating lobular carcinoma of the breast.

Thirty-eight breasts with lobular carcinoma in situ and an additional intraductal or infiltrating cancer were studied. Twenty-six of the additional cancers were diagnosed as infiltrating lobular cancer on the basis of a single population of small uniform cells cytologically identical to those in lobular carcinoma in situ. In 20 of these cases the conventional pattern of infiltrating lobular cancer was evident with an individual cell infiltrate with foci of single filing. In the other six there was a confluent arrangement of cells in solid sheets. This pattern has not been previously reported as a pattern of infiltrating lobular cancer. Because of the identical cytologic appearance, we believe it is a variant of infiltraing lobular cancer and should be diagnosed as such.