Radiotherapy appears to be an essential component of the optimal treatment regimen for adults with early-stage favorable Hodgkin lymphoma, investigators in a randomized phase 3 trial asserted.
Among more than 600 patients with early-stage Hodgkin lymphoma who were positron-emission tomography (PET)–negative after two cycles of standard chemotherapy, 5-year progression-free survival was significantly better for patients who had also received involved-field radiotherapy, compared with those who had received chemotherapy alone.
The HD16 trial was designed to show whether using PET findings to opt for consolidation radiotherapy could be noninferior to the use of combined modality therapy (CMT) with ABVD (doxorubicin, bleomycin, vinblastine and dacarbazine) and radiation for all patients with early-stage favorable-risk disease.
“However, we failed to meet the primary objective of the trial as PET-guided omission of radiotherapy results in poorer tumor control compared with CMT. We therefore recommend proceeding with consolidation radiotherapy as a standard of care for patients achieving a metabolic response after two cycles of ABVD,” Michael Fuchs, MD, from the University Hospital of Cologne, Germany, and colleagues in the German Hodgkin Study Group wrote in the Journal of Clinical Oncology.
The investigators also found that patients who remained PET-positive after two cycles of ABVD were at high risk for treatment failure, particularly when a Deauville score of 4 was used as the minimum threshold for positivity.
Although CMT is associated with high cure rates for patients with Hodgkin lymphoma, clinicians are concerned about long-term toxicities and risk for second malignancies, which prompted investigators to see whether radiotherapy could be safely eliminated in some cases.
The HD16 investigators enrolled 1,150 patients aged 18-75 years with early-stage favorable Hodgkin lymphoma, and randomly assigned them to receive two cycles of ABVD with either 20 Gy of involved-field radiotherapy or PET-guided treatment in which involved-field radiation was eliminated for those patients who were PET-negative after chemotherapy, with PET negativity defined as a Deauville score less than 3.
After a median follow-up of 47 months, the 5-year progression-free survival rates among 628 PET-negative patients were 93.4% for those assigned to CMT, versus 86.1% for patients assigned to chemotherapy alone, which translated into a hazard ratio HR of 1.78 (95% confidence interval, 1.02-3.12; P = .040). The upper limit of the confidence interval exceeds the predefined noninferiority margin of 3.01, which indicates that eliminating radiation was clinically inferior.
The difference in progression-free survival rates between the treatment arms was primarily caused by a significant increase in disease recurrence in what would have been the involved field for patients in the ABVD-alone group (in-field recurrence rate, 9% vs. 2% for patients who received CMT; P = .0003). In contrast, there were no significant differences between the groups in out-of-field recurrences (5% vs. 4%, respectively).
Five-year overall survival rates were virtually identical between the treatment arms among PET-negative patients.
When the investigators compared all PET-negative with PET-positive patients (Deauville score 4), they saw that 5-year estimated progression-free survival rates were 93.1% vs. 80.9%, respectively, an absolute difference of 12.1% that translated into a HR of 2.94 (P less than .001). There were no significant differences by PET status in 5-year overall survival, however.
“We assume that the small radiation fields and doses used in our HD16 trial will induce fewer late adverse events than those reported in the literature. However, we cannot exclude an increased risk for certain late effects, such as breast cancer in very young women, as the risk for this specific second malignancy increases with younger age,” the researchers wrote.
The study was supported by grants from Deutsche Krebshilfe and the Swiss State Secretariat for Education, Research, and Innovation. Dr. Fuchs reported honoraria from Amgen, Affimed, Celgene, and Takeda. Multiple coauthors reported industry funding.
SOURCE: Fuchs M et al. J Clin Oncol. 2019 Sep 10. doi: 10.1200/JCO.19.00964.