Morphological characteristics of invasive lobular carcinoma and its variants. (A) Low power view of a terminal duct lobular unit colonised by lobular carcinoma in situ. Classic invasive lobular carcinoma is seen diffusely infiltrating the whole specimen as single cells and single files of cells. The characteristic targetoid growth pattern is evident on the left-hand side (see also Figure 2). (B-G) Morphological variants of the classic type: (B) alveolar type, with globular aggregates of approximately 20 cells; (C) solid type with discohesive tumour cells growing in solid sheets; (D) a pleomorphic variant - note the pink, foamy cytoplasm typical of an apocrine phenotype and irregular nuclei; (E) pleomorphic invasive lobular carcinoma with prominent signet ring cells; (F) invasive lobular carcinoma showing mucinous/histiocytoid morphology; (G) mixed ductal-lobular carcinoma.