Background Breast-conserving surgery (BCS) is considered the gold standard of early stage invasive breast cancer treatment that achieves adequate surgical margins with an acceptable cosmetic outcome. The margin status is an important prognostic factor for local recurrence after BCS in patients with early breast cancer. The patients receiving BCS have a lifelong risk of local recurrence. To minimize this risk, a technique of margin evaluation, called cavity shaving or cavity margin shaving has been proposed and applied by some surgical teams to reduce the need for reexcisions and to detect multifocality. Patients and methods In the present prospective, randomized trial between August 2015 and August 2018, we assigned 40 women with breast cancer of stages 0–III who were undergoing partial mastectomy and divided into two groups; shave group and lumpectomy group. Excision of cavity shave margins consists of resection of breast tissue from four margins; superior, inferior, medial, and lateral after the excision of the primary specimen in the same procedure. We classified the margins as negative (>2 mm), close (<2 mm), or positive based on the distance from the tumor to the margin of resection. Results We have 40 patients in the current study. Overall, patients who underwent BCS plus cavity shaving had a higher rate of negative margins (92%) compared with patients who underwent BCS (66.7%). In shaving lumpectomy group (SLG), patients with negative margins before shaving were 15 (60%) versus 23 (92%) after shaving. All patients with positive margins (n=7) were offered a re-excision procedure. Conclusion Comparing to the lumpectomy alone, cavity margin shaving plus lumpectomy during BCS for early stage invasive breast cancer results in a higher rate of negative microscopic margins for tumor and a lower reoperation rate, although it increases the operation time, the resection volume. Keywords: breast carcinoma, breast-conserving surgery, cavity margin, lumpectomy, surgical margins