Gecacitinib for cGVHD: Safety and Efficacy in Patients After ≥2 Lines of Prior Therapy

Inclusion Criteria: * Voluntarily Signed informed consent and aged ≥18 years * Undergone nonmyeloablative, myeloablative, or reduced-intensity allo-HSCT using bone marrow, peripheral blood stem cells, or umbilical cord blood from any donor source * Confirmed myeloid and platelet engraftment: ANC \>1.0×10⁹/L and platelet count \>25×10⁹/L; no hematopoietic growth factors or blood product transfusions within 7 days before screening * Clinically diagnosed moderate-to-severe cGVHD according to the 2014 NIH * Received 2-5 prior systemic cGVHD therapies with persistent disease * ECOG PS score of 0-2 * Able to swallow tablets * Concomitant use of non-interacting immunosuppressants permitted Exclusion Criteria: * Recurrence of malignancy or loss of full donor chimerism * Concurrent use of other JAK inhibitors, mesenchymal stem cells, or belumosudil (Eligible if discontinued for \>8 weeks post-aGVHD treatment or stopped JAK inhibitors for cGVHD due to side effects.) * Severe pulmonary cGVHD (FEV1 ≤39% or NIH lung symptom score of 3) * Post-transplant lymphoproliferative disease * Significant abnormalities affecting safety assessment, such as uncontrolled hypertension (SBP ≥160 mmHg or DBP ≥100 mmHg) despite ≤2 antihypertensives; ALT/AST \>3×ULN; DBIL/TBIL \>1.5×ULN; serum creatinine \>1.5×ULN * History of major cardiovascular events within 6 months. * Arrhythmia requiring treatment at screening * Gastrointestinal conditions impairing drug absorption * Surgery within 4 weeks of screening with incomplete recovery * Active/uncontrolled infections (viral, bacterial, parasitic, fungal) requiring treatment * Active tuberculosis within 6 months * Epilepsy or use of psychotropic/sedative drugs * Pregnant/breastfeeding or unwilling to use contraception during and 4 weeks post-study * Malignancy within 5 years (except the indication for transplant) * Use of anticoagulants/platelet inhibitors (except low-molecular-weight heparin) * Herbal medicine use within 1 week prior to enrollment * Hypersensitivity to gecacitinib or its components * Participation in another clinical trial within 4 weeks (or 5 half-lives of the previous study drug, whichever is longer) * Deemed unsuitable by the investigator