Knowledge on the impact of neoadjuvant and adjuvant treatments on post-surgery lymphedema (LE) in patients with breast cancer is limited due to methodological limitations and an insufficient sample size. We investigated the risk of LE in patients going through long-term anticancer treatment regimens using a national cohort from the Korean National Health Insurance Service database from 2011-2013. Incidence rate ratio, Kaplan-Meier analysis, and Cox proportional regression analysis were performed. A total of 39,791 patients were included. While minimal lymph node dissection (SLNB) reduced the risk of LE (hazard ratio HR 0.51) as expected, neoadjuvant chemotherapy (NAC) followed by SLNB did not reduce the risk. Adjusting for adjuvant chemotherapy (AC) as time-varying exposure decreased the risk of LE in the SLNB group (HR 0.51), but not the mortality risk (HR 0.861). A longer duration of NAC, especially taxane-based, combined with SLNB reversed the effect and increased risk of LE. The findings highlight the importance of not only early surveillance before and after surgery, but also long-term surveillance during adjuvant treatment by surgeons and oncologists in order to reduce the risk of LE.