Clinicopathologic Features and Long-Term Outcomes of Adult Hypopigmented Mycosis Fungoides

Importance: Hypopigmented mycosis fungoides (HMF) is uncommon in adults, and data on clinicopathologic features and long-term outcomes remain sparse. Objective: To investigate the clinicopathologic features and outcomes of adults with HMF in a large multicenter cohort. Design, Setting, and Participants: This retrospective multicenter cohort study conducted from January 2011 to October 2023 at 6 US tertiary referral centers and included adults (18 years or older at diagnosis) with biopsy-confirmed HMF and hypopigmentation documented at diagnosis, with a median (range) follow-up of 39 (1-347) months. Data were analyzed from February to December 2025. Exposures: Clinical variant, immunophenotype predominance, and polymerase chain reaction-based T-cell receptor (TCR) gene rearrangement in peripheral blood and/or skin. Main Outcomes and Measures: Best overall response, defined as complete response, partial response, stable disease, or progressive disease, and progression to a higher stage. Results: The cohort included 224 adults with HMF (median [range] age, 44 [18-74] years), of whom 164 (73%) were women (60 men [27%]), 5 (2%) were Asian individuals, 1 (0.4%) was a Hispanic/Latino individual, 1 (0.4%) was a Middle Eastern individual, 19 (8%) were White individuals, and 186 (83%) were Black individuals; 219 (98%) presented with early-stage disease. Most had hypopigmented lesions only (159 [71%]), whereas 65 (29%) exhibited mixed-variant mycosis fungoides; outcomes were similar between groups. Among 141 patients with available immunophenotyping, 88 (63%) had CD8-positive predominance. Among 207 treated patients, most (179 [90%]) received skin-directed therapy alone. Among 198 evaluable patients, the best overall response was complete response for 52 (26%), partial response for 101 (51%), stable disease for 34 (17%), and progressive disease for 11 (6%). Over a median (range) follow-up of 39 (1-347) months, 14 of 224 patients (6%) experienced progression to a higher stage, including 5 of 219 patients (2%) with early-stage disease at baseline who experienced progression to advanced-stage disease. Peripheral blood TCR monoclonality was detected in 23 of 85 tested patients (27%) and was associated with poorer treatment response but not with disease progression. Conclusions and Relevance: The finding of this cohort study suggest that adult HMF demonstrated a generally indolent course, with favorable response to skin-directed therapy, irrespective of immunophenotype or mixed-variant presentation. Peripheral blood TCR monoclonality was associated with lower treatment response but not disease progression.