131. Vascularized Lymph Node Transplant Reduces Mast Cell Tissue Infiltration in Breast Cancer Related Lymphedema

PURPOSE: Secondary lymphedema poses a significant burden for breast cancer patients undergoing axillary surgery, with its management remaining challenging. Our lab has recently identified a correlation between increased local mast cell numbers in the skin, and greater clinical severity of breast cancer related lymphedema (BCRL), including higher arm volume differentials (%) and LDEX scores. However, the impact of treatment interventions on local mast cell populations remains unclear. Vascularized lymph node transplant (VLNT), a therapeutic option for patients with BCRL who are refractory to conservative therapies, is effective for the treatment of BCRL in most patients. This study aims to investigate the effect of VLNT on local mast cell numbers, and their relationship to clinical symptoms, in a cohort of BCRL patients. METHODS: Five patients with unilateral BCRL who underwent VLNT between April 2018 and January 2020 were included in the study. Matched arm skin specimens were collected at the time of VLNT, and 12-months post-operatively. Specimens were stained for mast cell tryptase, and immunofluorescence was compared between pre- and post-operative groups. Patients were closely monitored post-operatively, with clinical assessments of arm volume differential, LDEX scores and symptoms. RESULTS: VLNT was correlated with a significant histological reduction in mast cell number in the lymphedematous arm at 12-months post-operatively (r=0.977, p=0.0042). On average, patients experienced a 52.08% reduction in mast cell density (number/0.05mm2), compared to pre-operative levels (p=0.0027). All five patients showed a decrease in arm volume differential, from an average of 20.98% pre-operatively to 11.09% at 24-months post-operatively. LDEX scores also improved, dropping from an average pre-operative score of 20.98 to 12.94 post-operatively (p=0.0391). CONCLUSION: Our findings suggest that beyond providing symptomatic relief, VLNT results in a significant reduction in local mast cell populations, which may contribute to observed improvements in arm volume and LDEX scores. This reduction in mast cells may be a key mechanism underlying BCRL resolution, and offers additional insight into the therapeutic effects of VLNT.