Investigating the Local Effectiveness of Carbon Ion Radiotherapy for Unresectable Female Genital Tract Melanomas: A Preliminary Real-World Study.

Background/Objectives: Primary gynecological melanomas are rare malignancies with lower survival rates compared to cutaneous melanomas. Both preclinical and clinical data support the evidence that mucosal melanomas are photon-radioresistant but responsive to carbon ion radiotherapy (CIRT). The aim of this study is to assess, in a real-world cohort, the effectiveness and tolerability of radical CIRT in patients with inoperable gynecological mucosal melanoma. Methods: This is a real-world study aimed to assess the effectiveness and the safety of CIRT in this setting. We defined as the primary endpoints the objective response rate (ORR) and the clinical benefit (CB). The secondary endpoints included the actuarial local control rate (LC) assessed after 1 year and 2 years and the toxicity scored according to CTCAE v.5. Actuarial outcomes were analyzed using the Kaplan-Meier method, while potential predictors were investigated through the Log-rank test. Results: Between 2017 and 2023, eleven Caucasian patients underwent pelvic CIRT (total dose 68.8 GyRBE) for mucosal malignant melanoma of the vulva or the vagina. With a median follow-up of 18 months, we observed an ORR of 82% and a CB of 100%. LC at 1 and 2 years was 100% and 86%, respectively, and among the factors analyzed for their potential impact on LC, age < 60 years seems to be a potential predictor (p = 0.014). The treatment was well tolerated, with only one case of acute grade 3 erythema and, in the late phase, one case of grade 3 erythema and grade 3 urethral toxicity. Conclusions: CIRT was effective and safe for gynecological melanomas. Larger collaborative cohort studies and longer follow-ups are needed to take a step forward in comprehending the correct management of this disease.