Lymphedema (LE) is a chronic medical condition characterized by lymphatic fluid retention, resulting in tissue swelling. Cancer treatments involving lymph nodes can damage lymph drainage routes, causing accumulation of lymph fluid in the interstitial tissue of related limbs and body areas and secondary LE. Basically, the LE has a negative impact on physical and mental quality of life. Moreover, 0.07-0.04% of long term survivors (most patients undergoing mastectomy) can develop the Stewart-Treves syndrome, a rare and aggressive multifocal lymphangiosarcoma arising within the LE region. Here we describe the case of a 45-year-old woman with a massive LE of the left arm, as a consequence of previous breast cancer, who was diagnosed after 4 years of stage IV mantle cell lymphoma (MCL). The patient, after obtaining complete remission with chemotherapy and autologous hematopoietic stem cell transplant, had a relapse of MCL in the lymphedema site.