The primary objective of the investigators is to develop an integrated algorithm for surgical treatment of chronic lymphedema after breast cancer surgery. This will be achieved by retrospectively analysing a subgroup of patients who had breast cancer-related surgery prior to lymphedema.

Evidence-based surgical treatment recommendations for lymphedema post breast cancer surgery are practically non-existent. In fact, the meager literature on this matter takes into account only quality of life or patient reported outcome - if at all. In light of the heavy burden imposed upon a large portion of breast cancer survivors by chronic lymphedema, the investigators' study aims to create an evidence-based treatment protocol - "The Basel Lymphedema Protocol" - to guide surgeons in taking the best course of action when advising patients, engaging in shared-decision and performing surgery to reduce lymphedema post breast cancer treatment. Accordingly, one of the investigators' driving goals is to allow surgeons to one day be able consistently rely on hard data.

This study is ultimately based on the investigators' intent to further patient welfare. To this effect, creating an integrated algorithm based on concrete, tangible data will not only aid patients by leading to improved treatment of their chronic lymphedema and enabling higher quality of life, but it will also bolster access to adequate coverage. For at present, surgical treatment of lymphedema requires submitting a request for a commitment to cover costs to health insurance providers. This is a protracted, tedious and - unfortunately - an oftentimes fruitless endeavour. However, by having a strong factual basis - more scientific data and peer-reviewed studies - such requests gain a much greater chance of success. To this end, the current study certainly has the capacity to pave the way and set evidence-based standards. And lastly, the creation and implementation of "The Basel Lymphedema Protocol" would strongly reflect the tenets and purpose of personalized/precision medicine - treatment tailored to the unique patient - and by so doing, refine resource allocation and cost-effectiveness of the healthcare system.

Inclusion Criteria:

• status post breast cancer or status post another type of cancer or status post no cancer
• chronic lymphedema - lymphedema lasting over three months - present prior to surgical treatment
• one type of surgical procedure for treatment of chronic lymphedema or a combination of surgical procedures for treatment of chronic lymphedema was performed
• one or any combination of the following surgical procedures was used in each individual patient: Lymph Node-Vein Anastomosis (LNVA) , Lymphaticovenous Anastomosis (LVA), Tumescent Liposuction (TL), Vascularized Lymph Node Transfer (VLNT) and/or Water-Assisted Liposuction (WAL)

Exclusion Criteria:

• inclusion criteria not met
• loss to follow-up (data not successfully collected)

Patients with lymphedema surgery performed at the University Hospital Basel between 2015 and 2023.