10527 Background: Arm lymphedema (ALE) is a serious consequence of the treatment for breast carcinoma. The objective of the current retrospective study was to analyze the time-course of minimal ALE after breast conservation treatment for early stage breast cancer. Methods: The study cohort was drawn from consecutive stage I or II patients who underwent breast conservation therapy including axillary staging followed by radiation. During follow up assessments after treatment, measurements of arm circumference were frequently performed at regular intervals, for clinically evident swelling of the arm or for complaints of swelling of the arm. ALE was documented in 274 of 1861 (15%) patients. 109 patients, 6% of overall group, and 40% of the patients with lymphedema, presented with minimal ALE, defined as a difference of 2 cm or less between the affected and unaffected arms. Results: The median age of patients was 54 years. The median interval to develop ALE was 1 year. The median follow up was 11 years. Among all 109 patients with minimal grade ALE at the time of ALE diagnosis, 21%, 13% and 14% of the patients progressed to more severe grades of lymphedema after 1,3 and 5 years of follow-up, respectively (See table). 40% of the patients with minimal grade ALE received therapy for lymphedema. Despite treatment for minimal grade ALE, 37% of treated patients progressed to more severe grades of lymphedema at 1 year follow up, and 24% progressed at 3 and 5 years follow up. Conclusions: Minimal ALE after breast conservation therapy, including axillary staging, developed in 6% of stage I or II breast cancer patients. Minimal ALE has the potential to progress to more severe grade of ALE. Despite treatment for lymphedema for minimal grade ALE, some patients still progressed to more severe grades of lymphedema. [Table: see text] No significant financial relationships to disclose.