Adult T-cell Leukemia/Lymphoma (ATL) is a highly aggressive T-cell malignancy that occurs in a proportion of individuals who are long-term carriers of Human T-cell Lymphotropic Virus type 1 (HTLV-1). Allogeneic hematopoietic stem cell transplantation has been suggested as a potentially curative strategy to eradicate HTLV-1 positive cells.

To describe the case of a patient with ATLL initially treated as peripheral T lymphoma and presenting refractoriness to several lines of treatment who was successfully treated with an allogeneic haploidentical stem cell transplantation.

A 60-year-old woman was diagnosed with peripheral T-cell non-Hodgkin lymphoma after a biopsy of skin lesions in December 2021. She did not present with lymphadenopathy. She was treated at another center with 6-cycles of Brentuximab Vedotin (BV), cyclophosphamide, doxorubicin and prednisone (BV-CHP) followed by autologous hematopoietic stem cell transplantation as consolidative therapy. Six months after transplant, she progressively presented worsening of her skin lesions. A new skin biopsy confirmed relapse, and she was referred to our center. A new skin biopsy revealed a diagnosis of T-cell lymphoma associated with a positive serology for the Human T-Lymphotropic virus 1 (HTLV-1). The combination of the biopsy findings and the association with HTLV-1 positivity supported the diagnosis of ATL. The patient achieved a complete response after 2-cycles of the association of BV, gemcitabine and oxaliplatin (Bv-Gemox), followed by a haploidentical allogeneic bone marrow transplant in July 2023. Her HCT-CI score was 1. The donor was her son, with a major ABO mismatch. Both were Cytomegalovirus (CMV) seropositive, and there were no HLA donor-specific antibodies. The reduced-intensity conditioning regimen consisted of fludarabine, cyclophosphamide, and Total Body Irradiation (TBI) 4 Gray, and the Graft-Versus-Host Disease (GVHD) prophylaxis was Post-transplant Cyclophosphamide (PtCy), sirolimus, and mycophenolate mofetil. Peripheral blood was the graft source with a 3.49×10̂6 CD34/Kg cell dose. Neutrophilic and platelets engraftment occurred at D+24 and D+41, respectively. She developed acute skin GVHD, which was successfully treated with topical steroids. She had CMV reactivation at low viral loads and did not require treatment. Sirolimus was withdrawn on D+70. Three months after transplant she presented disease relapse in an intraparotid lymph node, and BV was indicated. After 6 cycles, the patient achieved a complete response and BV was stopped. The patient developed chronic GVHD of the skin and mouth well controlled with topic steroids. In her last follow-up visit (13-months post-transplant), the patient remains in complete response and no systemic immunosuppression.

This case highlights the potential of haploidentical HSCT as a viable and effective treatment for patients with refractory ATL. Successful management of associated complications and the use of post-transplant BV to achieve sustained remission highlights the importance of multidisciplinary care and targeted therapeutic strategies to improve outcomes of allogeneic HSCT as a curative approach for patients with this T-cell lymphomas.