Initial diagnosis of breast cancer via cytological examination of a pleural effusion: a rare event facilitated by recognition of an unusual morphological pattern.

It is uncommon for breast carcinoma to present as a malignant serous effusion. Here, we describe a case in which the initial diagnosis of an occult invasive ductal carcinoma of the breast was made via cytological examination of a pleural effusion. Recognition of a cribriform architecture with intraluminal necrosis and microcalcifications in a cell block preparation was critical in making that diagnosis. To our knowledge, this specific morphological pattern of breast carcinoma in a cell block preparation from an effusion has not been reported previously.