In order to investigate whether lobular phenotype is indeed a rare variant of extracellular mucin-producing carcinoma of breast, we also studied tissue microarrays of 80 breast carcinomas with mucinous differentiation, including 40 pure mucinous carcinomas and 40 carcinomas with mixed mucinous and non-mucinous components. The gene discussed is MUC5AC; the disease is mucinous adenocarcinoma.