Cellularity of lobular carcinoma and its relationship to false negative fine needle aspiration results

OBJECTIVE: To evaluate the cytocellularity and histocellularity of lobular carcinoma (LC) and the relationship to high false negative results of fine needle aspiration cytology (FNAC). STUDY DESIGN: In this retrospective study, cellularity was studied in 60 cases of classic LC, LC variants and lobular carcinoma in situ, comparing cytologic smears to their corresponding histologic sections. The cytologic smears were grouped into acellular, low, moderate and high categories, and the histologic sections were grouped into low, moderate and high categories. RESULTS: Malignancy or suspicion of malignancy was diagnosed in 78% of cases. Overall cytocellularity showed acellularity or low cellularity in 60% of cases, while overall histocellularity showed moderate or high cellularity in 95% of cases. When the cytocellularity was moderate or high, the corresponding histocellularity always showed moderate or high histocellularity. When the cytocellularity was low, the corresponding histology showed low histocellularity in 6.3% of cases. Thus, in acellular and low cellular aspirations, corresponding histocellularity may not be the contributing factor toward low cellular yield. In this study, 22% of cases were diagnosed as false negative, 40% were diagnosed as suspicious, and 38% were called positive. Only 17% of positive cases were diagnosed as LC. A large number of LC were misdiagnosed by FNAC as duct cell carcinoma, and most cases of low histocellularity were of the classic type. CONCLUSION: The results of this study suggest that in the majority of cases of LC, cellular yield of FNAC is disproportionately lower than expected when compared to the corresponding histocellularity. Awareness of modest cellularity and subtle cytologic features will aid in the correct preoperative diagnosis of LC, and false negative diagnoses can be minimized.