Background: We report extended follow-up of TROG99.03, a randomised phase III trial in early-stage follicular lymphoma (ESFL) including new information on the role of adjuvant rituximab and translational studies. Methods: Patients with ESFL were randomised to involved-field radiotherapy (IFRT) or IFRT plus 6-cycles cyclophosphamide/vincristine/prednisolone (IFRT+CVP). From 2006 rituximab was added to IFRT+CVP (IFRT+R-CVP). Clinical and multi-omic parameters were evaluated. Findings were validated in two independent ESFL cohorts (99 and 60 patients respectively). Findings: Between 2000-2012, 150 (75 per arm) patients were recruited. 48% were positron emission tomography (PET)-staged. Per protocol, at median follow-up 11.3-years, progression-free survival (PFS) remained superior for IFRT+(R)CVP vs. IFRT (hazard ratio [HR]=0.60, 95%CI=0.37-0.98, p=0.043; 10-year PFS 62% vs. 43%) respectively. Although no significant difference in overall survival was observed (HR=0.44, 95%CI=0.16-1.18, p=0.11, 10-year OS 95% vs 84%), patients receiving IFRT+(R)CVP experienced fewer composite (histological transformation and death) events (p=0.045). PFS of IFRT+R-CVP-treated patients compared with all other treatments lacking rituximab (IFRT alone plus IFRT+CVP) was superior (HR=0.36, 95%CI=0.13-0.82, p=0.013). Amongst PET-staged patients, PFS differences between IFRT+R-CVP vs. IFRT were maintained (HR=0.38, 95%CI=0.16-0.89, p=0.027) indicating benefit distinct from stage migration. FL-related mutations and BCL2-translocations were not associated with PFS. However, by multivariate analysis elevated CD8A gene expression in diagnostic biopsy tissue was independently associated with improved PFS (HR=0.45, 95%CI=0.26-0.79, p=0.037), a finding confirmed in both ESFL validation cohorts. CD8A gene expression was raised (p=0.02) and CD8+ T-cell density higher within follicles in ESFL vs. advanced-stage FL (p=0.047). Human leucocyte antigen class I specific neoantigens were detected in 43% of patients, suggesting neoantigen-specific CD8+ T-cells have a role in confining the spread of the disease. Interpretation: Adjuvant R-CVP and elevated intratumoural CD8 expression were independently associated with sustained disease control after radiotherapy in ESFL. Funding: Cancer Council Victora; National Health and Medical Research Council; Leukaemia Foundation; Mater Foundation.

The authors have declared no competing interest.

NCT00115700

https://doi.org/10.1200/JCO.2018.77.9892

This trial received primary funding from the Cancer Council of Victoria with additional funding contributed by the Australasian Leukaemia and Lymphoma Group Peter MacCallum Cancer Centre Amgen and Roche. Roche also supplied the rituximab used in the amended version of the trial. QA for the trial was supported by a grant from the Australian Federal Department of Health.

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