PET-Guided Treatment of Early-Stage Favorable Hodgkin Lymphoma: Final Results of the International, Randomized Phase 3 Trial HD16 By the German Hodgkin Study Group

Background. Combined modality treatment (CMT) consisting of two cycles of ABVD (doxorubicin, bleomycin, vinblastine, dacarbazine) and 20 Gy of involved-field radiotherapy (IFRT) is widely accepted standard of care for early-stage favorable Hodgkin lymphoma (HL). Recent clinical research suggests that metabolic response assessment after two cycles of chemotherapy using FDG-PET (PET-2) can predict the individual outcome and PET-2 negativity might allow reducing the overall treatment intensity.

Aims. We assessed whether omitting consolidating radiotherapy in patients with negative PET-2 is feasible without loss of efficacy as determined by progression-free survival (PFS). Furthermore, we analyzed the prognostic impact of PET-2 among patients receiving CMT.

Methods. Between November 2009 and December 2015, we recruited patients with newly diagnosed, early-stage favorable HL aged 18-75 years from Germany, Switzerland, Austria, and the Netherlands for this double-blind, randomized, parallel-group phase 3 trial. Patients were randomly assigned to receive standard CMT with 2x ABVD and 20 Gy IFRT or PET-guided treatment, whereby IFRT was restricted to those patients with a positive PET after 2xABVD. PET-2 was centrally assessed by a panel blinded towards the randomization result, with FDG uptake not higher than the mediastinal blood pool (i.e., Deauville score 1-2) defined as negative. The trial was designed to exclude inferiority of 10% or more in 5-year PFS of ABVD only compared with CMT in a per-protocol analysis among PET-negative patients, corresponding to a non-inferiority margin of 3.01 for the hazard ratio, and to detect a 5-year PFS difference of 5% or more between PET-2-positive and -negative patients receiving CMT, each with 80% power.

Results. A total of 1150 patients were enrolled; 628 patients with negative PET-2 were eligible for the per-protocol non-inferiority analysis and were treated with CMT (n=328) or ABVD alone (n=300). With a median follow-up of 47 months, the estimated 5-year PFS was 93.4% (90.4-96.5) with CMT and 86.1% (81.4-90.9) with chemotherapy only (difference 7.3%, 95% CI 1.6%-13.0%). The hazard ratio was 1.78 with a 95% CI ranging from 1.02 to 3.12, including the non-inferiority margin of 3.01. The PFS difference primarily resulted from a significant increase in disease recurrences with in-field recurrence rates of 2.1% vs. 8.7% (p=0.0003); there was no relevant difference regarding out-field recurrences (3.7% vs. 4.7%, p=0.55). Estimated 5-year overall survival in the per-protocol population was 98.1% (96.5-99.8) with CMT and 98.4% (96.5-100.0) with ABVD.

693 patients assigned to receive CMT were eligible for the analysis of the PET objective and had a negative (n=353) or positive (n=340) PET-2. With a median follow-up of 46 months, estimated 5-year PFS was 93.2% (90.2-96.2) among PET-2-negative and 88.1% (83.8-92.3) among PET-2-positive patients (p=0.035). When using the more common liver cutoff (Deauville score 4) for the definition of PET-2 positivity, the difference was more pronounced (5-year PFS 93.1% [90.7%-95.5%] vs. 80.1% [71.2%-88.9%], p=0.0004).

Conclusion. In early-stage favorable HL, radiotherapy cannot be safely omitted from standard CMT without a clinically relevant loss of tumor control in patients with negative PET-2. PET positivity after 2xABVD represents a risk factor for PFS in HL patients treated with standard CMT, particularly when a Deauville score of 4 is considered as cutoff for positivity.