Adoptive Cell Transfer of Tumor-Infiltrating Lymphocytes for Metastatic Acral Lentiginous Melanoma

PURPOSE Acral lentiginous melanoma is a subtype of cutaneous melanoma arising from palmar, plantar, or subungual skin. These tumors are characterized by aggressive biology, a low tumor mutational burden (TMB), and diminished sensitivity to immune checkpoint blockade. It is unknown whether adoptive cell transfer of tumor-infiltrating lymphocytes (ACT-TIL) has efficacy in patients with acral melanoma. METHODS We analyzed prospectively collected data from 442 patients with metastatic cutaneous melanoma who were treated on clinical trials of ACT-TIL at a single institution between 1999 and 2018. Although blinded to treatment outcome and genomic data, we retrospectively identified patients who had acral subtype on the basis of clinicopathologic data available at the time of diagnosis. We then evaluated the ACT-TIL treatment outcomes of patients with acral melanoma and compared them with contemporaneously treated patients with nonacral melanoma. RESULTS Out of 442 included patients, 30 (7%) had acral melanoma while 412 (93%) had nonacral melanoma. Cohorts had similar clinical characteristics, protocol enrollment, and treatment-related factors. The objective response rate to ACT-TIL in patients with acral and nonacral melanomas was 43% and 40%, respectively ( P = .87), with 3% and 16% having complete responses (CRs; P = .07). Median progression-free survival was 3.5 and 4.1 months ( P = .40) and median overall survival was 13 and 17 months ( P = .79), respectively. Acral melanomas had lower TMB and ultraviolet mutational signature scores than nonacral melanomas. CONCLUSION ACT-TIL can mediate objective responses in patients with metastatic acral melanoma, and outcomes in patients with acral disease were unexpectedly comparable with those of contemporaneously treated patients with nonacral cutaneous melanoma. Further research is necessary to understand the immunologic basis of responses to ACT-TIL in acral melanoma and to increase the frequency of CRs.