Abstract P041

INTERIM AND END-OF-TREATMENT (EOT) PET/CT ASSESSMENT AFTER NIVOLUMAB, DOXORUBICIN, VINBLASTINE, AND DACARBAZINE (N-AVD) IN ADVANCED-STAGE CLASSICAL HODGKIN LYMPHOMA (CHL): A SINGLE-CENTER EXPERIENCE

Background: Based on the randomized SWOG S1826 trial, N-AVD demonstrated superior disease control compared with BV-AVD in stage III/IV classical Hodgkin lymphoma. We adopted N-AVD as first-line therapy for advanced cHL starting in July 2023. Although PET/CT is a cornerstone of response assessment in cHL, checkpoint inhibitors may increase false-positive (FP) findings. We evaluated our institutional experience with PET/CT after first-line N-AVD. Methods:We retrospectively analyzed patients with cHL treated with first-line N-AVD. Interim PET (iPET) after 2 cycles and end-of-treatment (EoT) PET/CT were assessed according to the Deauville Score (DS), with DS4-5 considered positive.

Results: Median age was 29 years (range 16–79), 13% were ≥60 years, 51% were male, 44% had B symptoms, 63% had nodular sclerosis, and 64% had stage IV disease. Four patients (10%) had positive iPET, all DS4; three converted to negative EoT scans, suggesting FP iPET findings, whereas one developed progressive disease confirmed by subsequent PET/CT (DS5) having received BrECADD after N-AVDx3. Among 36 iPET-negative patients, 7/36 (19%) had positive PET/CT (5 with DS4, 2 with DS5). Three DS4 cases became negative on repeat imaging after three months, while two DS4 and two DS5 cases represented true treatment failure confirmed by serial imaging and/or biopsy. Salvage treatment included BrESHAP followed by autologous stem-cell transplantation in two patients and radiotherapy for localized disease in one patient. One DS5 case was ultimately diagnosed as metachronous diffuse large B-cell lymphoma necessitating chemotherapy initiation. An additional patient relapsed within 12 months despite negative iPET and EoT PET/CT. Overall 6/40 patients have experienced treatment failure so far (15%). With a median follow-up of 20.7 months, estimated 2-year progression-free survival was 82%.

Conclusions: N-AVD demonstrated high efficacy with a low rate of iPET positivity and no interim DS5 scans. Interestingly, most treatment failures occurred despite negative iPET, whereas several EoT-positive scans proved false positive, highlighting the limitations of PET/CT interpretation after checkpoint inhibitor-based therapy. Therefore, PET/CT results should be evaluated within the broader clinical context, and isolated metabolic findings should not automatically prompt treatment modification without careful consideration.