Undetected invasive lobular carcinoma of the breast: review of false-negative smears.
Analysis of a series of 34 fine-needle aspirations (FNA) from 28 patients with invasive lobular carcinoma (ILC) was undertaken. The false-negative smears were reviewed to reveal the cause of such a relatively frequent error. This was a retrospective study and comparison between the cytological and pathological findings in a series of 34 FNA. Three cases were excluded without sufficient material. Twelve cases were positive, nine suspicious of malignancy, and 10 were considered false-negatives. In a second analysis of this later group, one was reclassified as carcinoma, two reconsidered without sufficient material for diagnosis, and the remaining seven, still considered negatives, constituted the core of this study. Of these seven, there were none with hypercellular smears and in six there was a predominance of fat-tissue fragments. The scarce epithelial component showed honeycomb-flat sheets in four, loose clusters in three, small and tight clusters with irregular limits in six, and more than 10% of isolated epithelial cells (noncohesive cells) in one case. "Staghorns" were undetected and myoepithelial cell nuclei were very scarce in all cases. Some nuclear enlargement was detected in one, angulated nuclear contour in three, and nuclear crowding was present in five. All seven had fine, homogeneous chromatin, without prominent nucleoli. Cytoplasmic limits were undefined in all but one (6/7) and occasional cytoplasmic vacuolization was detected in two. Hypocellular smears with few, small, and dense groups (but always with more than 10 groups in at least one smear) can be related with ILC. In these cases, further studies are recommended to exclude malignancy. The loose cluster and flat sheets identified in four cases represent a benign epithelial hyperplasia mixed with the ILC.