Myoepithelial Cells: Any role in aspiration cytology smears of breast tumors?

AIMS AND OBJECTIVE: To study the role of myoepithelial (ME) cells in distinguishing benign, proliferative breast diseases (PBD) and frank malignant breast lesions. MATERIALS AND METHODS: In this study, histology proven 71 cases of fine needle aspiration cytology (FNAC) of palpable breast lesions were selected. There were 30 invasive carcinomas (24 infiltrating duct carcinoma and 6 infiltrating lobular carcinoma), 25 cases of benign lesion (21 fibroadenomas and 4 fibrocystic lesions) and 11 proliferative breast diseases (other than carcinoma in situ) and five cases of carcinoma in situ. The number of ME cells were estimated in respect to 1000 ductal cells. In every case at least 20 high power fields (× 40) were studied. Quantitative estimation of ME cell was correlated with the final diagnosis. Corresponding histopathology cases were also evaluated for diagnostic confirmation along with the pattern of distribution of ME cells. The ME cells were also quantitated on histopathology sections on smooth muscle actin (SMA) immunostained sections. RESULTS: The mean number of ME cells per 1000 ductal cells on cytology smears was 5.1 ± 5.5, 30.8 ± 25, 28.3 ± 20.2, and 38.4 ± 38.8 in malignant, carcinoma in situ, PBD and benign breast lesions respectively. The non parametric Mann Whitney test showed significant difference in number of the ME cells between benign and malignant groups (p < .000), PBD and malignant groups (p < .000) and carcinoma in situ and malignant group (p < .001). However, it was insignificant between benign and PBD group, and PBD and carcinoma in situ (p > .01). In SMA stained histopathology sections, ME cell in benign, PBD, carcinoma in situ and malignant cases were 741.12 ± 248, 238 ± 172, 121.6 ± 115 and 15.6 ± 25.1 respectively. Statistical analysis showed significantly different number of ME cell between benign versus PBD group, carcinoma in situ and malignant group. It was also significant between PBD versus malignant, and carcinoma in situ versus malignant (p < .001, Mann Whitney test). However number of ME cell was not significant between PBD versus carcinoma in situ. CONCLUSION: The number of ME cell in breast lesions may be helpful in distinguishing PBD versus invasive malignant tumors on FNAC smears. However it is not helpful to distinguish benign lesions versus PBD.