Eosinophils in metastatic melanoma

The potential significance of tissue eosinophils melanomas is unknown. We strove to determine a potential association between the presence of tissue eosinophils and prognosis of patients with metastatic melanoma (MM). A retrospective electronic data base was queried to identify patients (age ≥18 years) evaluated January 1, 2011-October 1, 2022 (inclusive) at our multi-site medical center, who had metastatic melanoma and at least 1 biopsy of melanoma or a melanocytic nevus that was reported to show eosinophils. Patient demographics, histopathological tumor features, AJCC classification parameters, and peripheral blood eosinophilia (PBE) obtained during the patients' routine care were recorded. Seven patients met inclusion criteria had checkpoint inhibitor therapy for MM; 4/7 had prominent eosinophil infiltrates among their melanocytic nevi or/and melanomas, and all had absent or less than predicted tumor progression. In our small cohort of patients undergoing immunotherapy for metastatic melanoma, the presence of tissue eosinophils among nevi or melanomas was associated with a favorable response. While lymphocytes have been considered key in the host response to melanoma, the role of eosinophils may be underappreciated.