Patterns of Initial Relapse from a Phase 3 Study of Response-Based Therapy for High-Risk Hodgkin Lymphoma (AHOD0831): A Report from the Children's Oncology Group.

PURPOSE: The Children's Oncology Group protocol AHOD0831, for pediatric patients with high-risk classical Hodgkin lymphoma (cHL), used response-adapted radiation fields, rather than larger involved-field radiation therapy (IFRT) that were historically used. This retrospective analysis of patterns of relapse among patients enrolled in the study was conducted to study the potential effect of a reduction in RT exposure. METHODS AND MATERIALS: From December 2009 to January 2012, 164 eligible patients under 22 years old with stage IIIB (43%) and stage IVB (57%) enrolled on AHOD0831. All patients received 4 cycles of doxorubicin, bleomycin, vincristine, etoposide, prednisone, and cyclophosphamide (ABVE-PC). Those patients with a slow early response (SER) after the first 2 ABVE-PC courses were nonrandomly assigned to 2 intensification cycles with ifosfamide/vinorelbine before the final 2 ABVE-PC cycles. Response-adapted RT (21 Gy) was prescribed to initial areas of bulky disease and SER sites. Rapid early response (RER) sites without bulk were not targeted. Imaging studies at the time of progression or relapse were reviewed centrally for this retrospective analysis. Relapses were characterized with respect to site (initial, new, or both; and initial bulk or initial nonbulk), initial chemotherapy response, and radiation field (in-field, out-of-field, or both).
RESULTS: Of the entire cohort, 140 patients were evaluable for the patterns of failure analyses. To investigate the pattern of failure, this analysis focuses on 23 patients who followed protocol treatment and suffered relapses at a median 1.05 years with 7.97-year median follow-up time. These 23 patients (11 RER and 12 SER) experienced a relapse in 105 total sites (median, 4; range, 1-11). Of the 105 relapsed sites, 67 sites (64%) occurred within an initial site of involvement, with 12 of these 67 sites (18%) at an initial site of bulky disease and 63 of these 67 relapses (94%) occurring in sites that were not fluorodeoxyglucose (FDG)-avid after 2 cycles of ABVE-PC (PET2-negative). Of the 105 relapsed sites, 34 sites (32%) occurred in a new site of disease (that would not have been covered by RT); and, overall, only 4 of 140 patients (2.8%) (occurring in 3 RER and 1 SER) experienced isolated out-of-field relapses that would have been covered by historical IFRT.
CONCLUSIONS: For a cohort of high-risk patients with cHL patients, most failures occurred in nonbulky, initially involved sites, largely due to response-based consolidation RT delivered to patients with bulky disease. In this analysis, we discovered low rates of failures outside of these modern risk-adapted radiation treatment volumes. Also, FDG uptake on PET2 did not identify most relapse sites.