Safety and efficacy of topical imiquimod use in allogeneic hematopoietic stem cell transplant recipients: A multicenter retrospective analysis

Summary: This study assesses the efficacy of imiquimod in allogeneic hematopoietic stem cell transplant (allo-HSCT) recipients and impact on flares of mucocutaneous graft-versus-host disease (GVHD) at application sites. A retrospective analysis of allo-HSCT recipients treated with imiquimod at Brigham and Women’s Hospital, Massachusetts General Hospital, and Dana-Farber Cancer Institute (01/2015–09/2024) was performed. Patients had at least three months of follow-up post-imiquimod. Among 54 allo-HSCT recipients treated with imiquimod, 39/54 (72.2%) had history of GVHD prior to initiation; 21/54 (38.9%) had active GVHD at treatment initiation. Localized GVHD flares occurred in 2 (3.7%) patients: one with oral GVHD following mucosal application for leukoplakia and one with sclerotic GVHD at cutaneous sites in the setting of concurrent immunosuppression taper and sunburn. Complete responses to imiquimod were observed in 0/3 (0.0%) leukoplakia, 6/16 (37.5%) superficial keratinocyte carcinomas, 7/18 (38.9%) warts, 1/9 (11.1%) cutaneous lymphoma, 1/1 (100%) leukemia cutis, 3/3 (100%) actinic keratosis, 0/2 (0.0%) vulvar intraepithelial neoplasia (VIN), and 1/2 (50%) molluscum contagiosum. GVHD exacerbation in areas of imiquimod use in allo-HSCT recipients appears to be infrequent but remains a potential risk. Mucosal application was the highest risk site for flaring mucocutaneous GVHD, with a flaring rate of 1/3 (33%). Clinicians should consider alternative topical therapy for mucosal sites, and if none exist, should be counseled on the risk of flaring mucosal GVHD. For cutaneous application, the majority (97.3%) tolerated imiquimod without flaring GVHD locally at application sites, with factors such as concurrent immunosuppression taper and sunburn contributing to the only case of localized cutaneous GVHD flare. Efficacy of imiquimod in allo-HSCT were lower than documented rates of efficacy reported in the literature for immunocompetent patients across multiple indications including leukoplakia and superficial keratinocyte carcinomas. Farrah L. Ezzeddine¹, Lauren Guggina¹, Connie Shi¹ 1. Dermatology, Brigham and Women's Hospital, Boston, MA, United States. Clinical Research: Epidemiology and Observational Research