#00065588

            A 59-year-old male patient presented to the dermatology department with purplish, erythematous nodular lesions that had initially appeared on the left side of his face and subsequently spread across his entire body over the past three months. A biopsy taken from lesions on the trunk and leg revealed acute leukemia infiltration and was reported as myeloid sarcoma. The patient was then referred to our department. Physical examination revealed widespread purplish, erythematous nodular lesions on the forehead, both sides of the face, trunk, back, and legs (Image 1-Left 4 panels). Additionally, lymphadenopathy measuring approximately 5 cm was detected in the right axillary region, and a 3-4 cm lymphadenopathy was palpated subcutaneously at the distal humerus level near the olecranon in the right upper arm. Histopathological slides from the external center were sent for a second-look evaluation at our hospital. Bone marrow aspiration and biopsy were performed. The second-look evaluation showed immunohistochemical positivity for TdT, CD33, CD4, CD43, CD123, and CD56 (in a few cells), consistent with atypical cell infiltration indicative of Blastic Plasmacytoid Dendritic Cell Neoplasm (BPDCN). Flow cytometry of the bone marrow revealed 21% CD45-positive blasts expressing CD56, CD81, CD123, and HLA-DR. The pathological report confirmed BPDCN infiltration. Contrast-enhanced CT scans of the neck, thorax, and pelvis showed lymphadenopathy in the right axilla, with the largest node measuring 80 mm in diameter. On November 18, 2024, treatment was initiated with Azacitidine (75 mg/m² for 7 days) and Venetoclax (100 mg). The venetoclax dose was gradually escalated to 200 mg and 400 mg. By day 15 of treatment, palpable lymph nodes had decreased in size. On day 21, response evaluation showed no blastic cells in the bone marrow, and flow cytometry reported a minimal residual disease of 0.01%. Cutaneous lesions had almost completely regressed (Image 1: Right 4 panels). Due to the absence of peripheral blasts, intrathecal therapy (IT) was planned. Cerebrospinal fluid cytology revealed disease involvement. On December 20, 2024, the patient received the first cycle of IT therapy, consisting of 40 mg Cytarabine, 12 mg Methotrexate, and 4 mg Dexamethasone. A total of 4 IT doses were administered twice weekly. On December 28, 2024, the second cycle of Azacitidine + Venetoclax chemotherapy was initiated and completed. HLA typing among relatives identified a fully matched (10/10) donor. Preparations for allogeneic HSCT were initiated and the patient underwent allogeneic stem cell transplantation. The patient is now being monitored at outpatient clinic in his 1^st month periodic follow up without any complication. In conclusion, BPDCN is an aggressive malignancy with low rates of complete response, even with high-intensity chemotherapy regimens. In this case, the patient achieved remission with low-intensity azacitidine-venetoclax therapy, enabling progression to allogeneic stem cell transplantation. This approach highlights the potential efficacy of low-intensity regimens in achieving remission in BPDCN and facilitating curative HSCT.

Image 1: Left 4 panels show the condition at the time of diagnosis, while right 4 panels depict the disease status following one cycle of Azacitidine-Venetoclax therapy