AbstractIntroductionHypersensitivity reactions (HSRs) to chemotherapy are serious adverse events associated with cancer drug therapy and can occur with any antitumor drug. This study investigated the safety and efficacy of carboplatin desensitization therapy in Japan and established a method for treating carboplatin HSRs.MethodsPatients diagnosed with gynecological (ovarian, endometrial, or cervical) cancers who underwent carboplatin desensitization therapy between 2016 and 2020 at the Gynecologic Cancer Study Group of Japan Clinical Oncology Group were included. The carboplatin desensitization therapy at each institution and the implementation cases were registered in an online case report form.ResultsThis retrospective study enrolled 136 patients (ovarian, 108; endometrial, 17; and cervical cancer, 11). Pre‐existing allergies were present in 37 (27.2%) patients, and 32 (23.5%) patients exhibited prodromal symptoms during treatment before HSR onset. Erythema was the most common symptom at HSR onset, affecting 93 (68.4%) patients, followed by itching in 72 (52.9%) patients and decreased oxygen saturation in 43 (31.6%) patients. Loss of consciousness occurred in three (2.2%) patients. The most common timing of HSR onset was during the first recurrence treatment (47%). The mean total carboplatin dose until HSR onset was 7331 (2620–18,282) mg, and the mean number of doses was 14 (4–63). Desensitization treatment was completed in 75% of cases, and breakthrough HSRs occurred in 25% (34/136). No deaths occurred in the study cohort. The risk factors for HSRs were not identified.ConclusionAlthough carboplatin desensitization therapy has high success rates in Japan, erythema and pruritus are important HSRs to consider.