Cytological Differentiation of Ductal Carcinoma in Situ and Invasive Ductal Carcinoma of the Breast: A Personal View and a Literature Review

Although some find it controversial, it is possible to differentiate breast ductal carcinoma in situ (DCIS) and invasive ductal carcinoma (IDC) using cytology only, with certain limitations. Invasiveness is the consequence of specific biological, i.e. aggressiveness potential of malignant cells, which is different with respect to the pre-existent DCIS, consequentially with different morphology. During the invasion, malignant cells go through multiple morphological changes, losing their epithelial and acquiring mesenchymal features in the fantastic process of epithelial-mesenchymal transition, which explains their morphology in cohabitation with the environment, includes the disruption of intercellular junctions, the increase of mobility and the release of the original epithelium. This mesenchymal-like phenotype supports the migration and invasion of cells, i.e. thus epithelial-mesenchymal transition ensures the tumor dissemination and metastasizing. Therefore, invasiveness can cytologically be “measured” by detecting morphological signs of increase of biological aggressiveness of malignant cells – through the change of their appearance (cytoplasm elongation in malignant squamous cells, i.e. in adenocarcinoma intracytoplasmic lumina, atypical nucleoli, coarsely clumped chromatin, eu-/parachromatin), but also with stromal parameters (disruption of the intercellular matrix, elastin fragments, capillaries endothelium) presented by tumour diathesis, fibroblast proliferation, fragments of elastoid stroma, invasion of connective and/or adipose tissue by groups and individual malignant cells. For the invasion are also very predictive tubular malignant structures, irregular angulated clusters of reduced cohesiveness, absence of benign naked nuclei, polymorph single tumour cells, less myoepithelial cells on tumour groups, fewer microcalcifications and foamy macrophages. Opposite morphological findings suggest DCIS. Even though cytologically we do not see and cannot see the basement membrane, highly likely we can predict the invasion – necessarily and always with the triple-diagnostic approach or clinical-radiological-morphological correlation to every breast lesion, in the representative well cellular sample and with good knowledge of patohistology and cytology