Residual specimen cellularity after neoadjuvant chemotherapy for breast cancer

Background: Neoadjuvant chemotherapy for breast cancer reduces tumour cellularity, the percentage of the primary tumour area that is composed of invasive tumour cells. Minimal residual tumour cellularity (5 per cent or less of tumour area composed of invasive tumour cells) may be associated with an increased risk of false-negative intraoperative margins. The aim of this study was to evaluate the incidence of minimal residual tumour cellularity after neoadjuvant chemotherapy and its impact on the frequency of false-negative margins and conversion from breast-conserving surgery to mastectomy. Methods: The final pathology slides of 510 patients who had surgery after neoadjuvant chemotherapy were reviewed. Results: Of 396 patients with residual invasive breast cancer after neoadjuvant chemotherapy, 100 specimens (25-3 per cent) had minimal residual cellularity; this was more frequent in patients with invasive lobular carcinoma (17.0 versus 5.1 per cent; P < 0.001) or well and moderately differentiated carcinoma (68.0 versus 52.4 per cent; P = 0.007). Among 149 patients who had initial breast-conserving surgery, false-negative intraoperative margin rates were 23 per cent in specimens with minimal and 13.8 per cent in those with higher residual cellularity (P = 0.210). There was no significant difference in the rate of conversion to mastectomy between the groups. Conclusion: Minimal residual cellularity after neoadjuvant chemotherapy occurred in about 25 per cent of specimens, but did not alter the rate of false-negative intraoperative margins.