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Invasive lobular carcinoma accounts for 5-10% of invasive breast carcinomas. This tumour is often bilateral and multicentric. Histologically, lobular carcinoma consists of infiltrating, small uniform cells with eccentrically placed, mildly hyperchromatic round nuclei and high N/C ratio. The cells can align themselves in a linear pattern or have a targetoid arrangement around ducts. Because of a prominent desmoplastic response, FNA smears can often be hypocellular.
Cytological diagnostic features
- Scanty to rich cellularity
- Small clusters, thin strands, cords, and single cells
- Uniform monotonous, relatively small cells with high N/C ratio
- Scanty cytoplasm, often indistinct
- Uniform, mildly hyperchromatic nuclei with mild to moderate irregularity
- Intracytoplasmic lumena, mucin vacuoles, and signet ring cells
- Stripped tumour nuclei
- No bipolar naked nuclei
Among breast malignancies, lobular carcinoma is the one which is most frequently associated with false-negative diagnoses, because of the bland cellular features and the often low cellularity. Invasive Lobular carcinoma may be confused with other types of breast carcinoma, especially when variants of lobular carcinoma are sampled (such as the solid, alveolar, mixed, or pleomorphic type). These cases are often misclassified as ductal carcinoma because of a greater cellularity or larger cells. It is not possible to distinguish definitively in situ from invasive lobular carcinoma, although invasive carcinomata are usually more cellular and discohesive with greater nuclear atypia. Similarly, the distinction between invasive ductal from invasive lobular carcinoma is not possible using cytology smears. This distinction will be performed on histopathology sections.