Predictors of Lumpectomy Size after Breast-Conserving Surgery in Patients with Breast Cancer: A Retrospective Cohort Study

Background: Oncoplastic reconstructive surgery as an extension of breast-conserving surgery leads to better aesthetic results, an increase in tumor-free margins, and a reduction in reexcision rates. Oncologic resection is often more extensive than expected, sometimes resulting in the plastic surgeon deviating from the predetermined plan. For optimal planning of the reconstruction, it is mandatory to estimate volume defects after lumpectomy as accurately as possible. The authors aimed to identify preoperative predictors of lumpectomy resection size. Methods: All consecutive patients diagnosed with invasive breast carcinoma or carcinoma in situ and treated primarily with breast-conserving surgery between 2018 and 2020 at the University Medical Center Utrecht or Alexander Monro Hospital were included. Patient and tumor characteristics were measured. Data were analyzed in a multiple linear regression analysis. Results: A total of 410 patients (423 cases) were included, with a median age of 58 years (range, 32 to 84 years) and a mean body mass index (BMI) of 25.0 (SD 9.3). The mean maximum radiologic tumor diameter was 18.0 mm (SD 13.2), and the mean maximum lumpectomy diameter was 58.8 mm (SD 19.2). Multiple linear regression analysis found an explained variance of R2 = 0.60 (P < 0.00), corrected for operating surgeon. Significant predictors for postoperative lumpectomy size were BMI, breast size, and maximum preoperative radiologic tumor diameter. A predictive tool for lumpectomy size was developed and a web-based application created to facilitate use of the tool in a clinical setting. Conclusions: Postoperative lumpectomy size can be predicted using BMI, breast size, and radiologic tumor size. This model could be beneficial for breast surgeons in planning reconstructions and preparing and informing their patients more accurately.