Invasive ductal carcinoma, Not Otherwise Specified (NOS)

Invasive ductal carcinoma is the most common type of breast carcinoma, accounting for approximately 75% of all invasive carcinoma. FNA specimens of ductal carcinoma, Not Otherwise Specified (NOS) usually show cytological features common to all breast carcinomata.

Cytological diagnostic features

• High cellularity
• Loosely cohesive groups and single atypical cells
• Syncytial arrangement with loss of polarity
• Tumour diathesis may be present
• Usually no bipolar naked nuclei
• Hyperchromatic nuclei, irregular and thickened nuclear membrane, nucleoli
• Increased N/C ratio

The malignant cells are usually much larger than benign ductal cells, although small cancer cells may occasionally be present. The background can vary from bloody or necrotic to clean. The smear cellular pattern is variable, with the malignant cells arranged in three-dimensional clusters, syncytial groups or occasionally acinar or gland-like patterns. The cells within the clusters show loss of polarity and nuclear moulding. The nuclei, which show malignant features, can be eccentrically placed, with a plasmacytoid appearance to the cells. The cytoplasm tends to be basophilic, finely to coarsely granular or finely vacuolated. Occasionally, cytoplasmic vacuolization or intracellular lumina can be seen. Signet ring cells may occasionally be seen, although they are more frequent in lobular carcinoma. Smears of poorly differentiated ductal carcinomas may contain pleomorphic, bizarre cells and multinucleated tumour cells.

FNA cytology is usually able to differentiate ductal from lobular breast carcinoma, although ductal carcinoma cells may occasionally be as small as cells from lobular carcinoma. Smears of ductal carcinoma are usually more cellular, with more significant pleomorphism, showing larger cells with hyperchromatic nuclei and more prominent nucleoli than lobular carcinoma cells.

Morphologic classification of breast carcinoma, which has a prognostic significance, can be applied to FNA specimens. Cytomorphological criteria are often able to diagnose the different histologic types on FNA smears, however the final classification can sometimes require examination of the surgically resected specimen. Cytological examination also allows nuclear grading of ductal carcinoma, which is prognostically significant.