Cytological characteristics of invasive lobular carcinoma of the human breast.

In contrast to invasive ductal carcinoma, invasive lobular carcinoma (ILC) of the breast is characterized by multiple ipsilateral occurrences and a higher incidence in the contralateral breast. It is therefore necessary to examine thoroughly whether there is any other carcinoma present before any breast-conserving surgery is carried out. We cytologically, histologically, and ultrastructurally investigated ILC and pure scirrhous carcinoma (PSC), a subtype of invasive ductal carcinoma, to establish cytological diagnostic criteria for the differential diagnosis of these two types of carcinoma that have high histological similarity. Cytologically, ILC cells showed linear or isolated cell arrangements and had small nuclei with round homogeneously distributed fine granular chromatin. The cytoplasm was light, and individual cells lacked cohesion. The carcinoma showed a rosary-like configuration. PSC cells, however, showed linear or cordlike arrangements. Individual cells showed a vertical arrangement. PSC cells had a linear cytoplasmic edge and were characterized by nuclear molding with coarse granular chromatin. These cytological findings were supported by histological and ultrastructural findings. These findings may contribute to histological estimation of ILC in preoperative cytological diagnosis.