Chronic graft-<I>versus</i>-host disease in the era of posttransplant cyclophosphamide.

Chronic graft-versus-host disease (cGVHD) remains a leading cause of late morbidity after allogeneic hematopoietic cell transplantation (HCT), but its phenotype under modern prophylaxis with post-transplant cyclophosphamide (PTCy) is not well characterized. We conducted a prospective, single-center study of 600 consecutive adults undergoing HCT with PTCy- based prophylaxis to assess incidence, clinical manifestations, treatment response, prognostic factors, and outcomes. Donors included matched siblings (36%), matched unrelated (34%), haploidentical (24%), and mismatched unrelated (6%). The 1-year cumulative incidence of moderate-to-severe cGVHD was 22% (95% confidence interval [CI]: 19-26%). The mouth was the most frequently involved organ (64%), with lichen planus-like changes as the predominant diagnostic feature, whereas sclerotic forms were uncommon. Notably, 27% of moderate-to-severe cases were managed successfully without systemic corticosteroids. The cumulative incidence of systemic therapy requirement was 15% at 1 year, with risk significantly higher in donors ≥30 years and in female-to-male transplants. Among 105 patients requiring systemic steroids, 64% achieved complete response, 32% discontinued immunosuppression, yet 18% developed cGVHD-related sequelae. Mouth ulcers and erythema, as well as a lung score ≥2 at steroid initiation independently predicted shorter failure-free survival. At 2 years, overall survival, cGVHD-free relapse-free survival, and GVHD-free relapse-free survival were 76% (95% CI: 72-79), 63% (95% CI: 60-68), and 57% (95% CI: 53-62), respectively. In conclusion, after HCT with PTCy-based prophylaxis, systemic therapy was required in only a minority of patients, with risk influenced by donor age and sex mismatch rather than donor type. While corticosteroids were generally effective, a substantial subset required salvage therapy, underscoring the burden of refractory cGVHD and the need for steroid-sparing approaches and novel interventions.