Precision of Mammogram and USG based evaluation of NAST response in breast cancer and its impact on oncoplastic surgery decisions

ABSTRACT Background Precise prediction of residual tumour size following neoadjuvant systemic therapy for breast cancer is crucial in assessing response and surgical decision making. Our study is aimed at assessing the performance of conventional imaging modalities like ultrasound and mammography in predicting the residual tumour size after neoadjuvant systemic therapy and in evaluating the impact of imaging on the surgical outcomes. Methods We retrospectively compared the tumour size measured by ultrasonography and mammography and the residual tumour size on final histopathology in 109 patients. Concordance was defined as a size difference within 25% of the histopathology size. We also looked at the distribution of concordance between different T status and molecular subtypes, accuracy of USG in predicting pathological complete response and axillary lymph nodal metastasis and also surgical outcomes in the discordant cases. Results The concordance rates of mammography and ultrasonography were 68.2% and 52.3% respectively without statistically significant difference between the two modalities (p = 0.081). Combination of both the modalities had a concordance rate of 57.8%. Ultrasonography had accuracy of 81.7% for predicting pathological complete response and 79.8% for predicting axillary nodal metastasis. We did not identify any influence of histologic subtype on the associations between preoperative measurements and pathology size or the accuracy for detecting pathological complete response (p values 0.43 and 0.46 respectively). In 12 cases, the radiology-pathology discordance could have led to large excision volume surgeries. In the overall cohort, recurrence free survival and overall survival rates at median follow up of 19.1 month were 87.2% and 95.4% respectively. Conclusions Ultrasound and mammography showed moderate concordance with pathology for estimation of the residual tumour size without any significant difference in the performance between the two. Despite the moderate concordance, surgical outcomes were fairly well managed in the discordant cases with the oncoplastic surgical techniques. Our study highlights the usefulness of the cheaper and widely available conventional imaging modalities in the developing countries where the cost of treatment is to be contained.