Breast cancer is the most common type of cancer among women globally and has the highest mortality rate. Surgical interventions are typically required in the treatment of breast cancer, but these procedures can lead to complications such as infection, seroma, hematoma, cellulitis, and particularly lymphedema due to disruptions in the physiology of axillary lymphatic vessels. Breast Cancer-Related Lymphedema (BCRL) commonly develops within the first two years following surgical intervention and its incidence varies depending on the surgical method used. The incidence of lymphedema after Sentinel Lymph Node Biopsy (SLNB) is around 5%, whereas it increases to 30-50% after Axillary Lymph Node Dissection (ALND). BCRL significantly impacts the quality of life (QoL) through physical symptoms such as swelling, pain, tightness, and limited range of motion, as well as psychosocial issues including depression, social isolation, and sleep disturbances. Sleep disorders, in particular, are associated with depression and contribute to a further decline in QoL. In the treatment of BCRL, both conservative (non-surgical) and surgical methods are traditionally employed. Complex Decongestive Physiotherapy (CDP) is considered the gold standard for the conservative management of lymphedema. CDP comprises a two-phase treatment process. The first phase, known as the Decongestion Phase, generally lasts 2-4 weeks and includes manual lymphatic drainage (MLD), skin care, compression therapy with multi-layered short-stretch bandages, and muscle-pumping exercises. The second phase, the Maintenance Phase, is more prolonged and aims to sustain the results achieved in Phase 1. It includes compression with low-stretch elastic garments, skin care, exercises, and patient-administered MLD as needed. The primary objectives of CDP are to improve lymphatic circulation, reduce swelling, pain, and tightness, increase the range of motion, and ultimately improve the QoL. Studies have shown that CDP significantly enhances sleep quality and QoL in women with BCRL. However, most existing studies examine all stages of BCRL without comparing the effects of CDP across different stages. The impact of CDP on sleep and QoL may vary depending on the stage of BCRL, highlighting the need for specific research on its effects in particular populations. Furthermore, many studies lack follow-up data, leaving the Maintenance Phase of CDP largely unexplored. This study aims to investigate the effects of CDP, including both the Decongestion and Maintenance phases, on sleep quality and QoL specifically in women with Stage II BCRL.