OUTCOME OF CURATIVE RADIOTHERAPY FOR LOCALISED FOLLICULAR LYMPHOMA IN THE ERA OF 18 F‐FDG PET‐CT STAGING: AN INTERNATIONAL COLLABORATIVE STUDY ON BEHALF OF ILROG

Abstract

Introduction: Most patients (pts) with follicular lymphoma (FL) present with advanced disease and are generally considered incurable. For the minority with localised disease, radiotherapy (RT) can be curative, with historical series showing a 10 year disease free survival of 40%‐50%. PET‐CT with 18F‐flurorodeoxyglucose is considered the gold standard imaging technique for staging FL. Compared to CT, upstaging occurs in 10‐60% of pts.We evaluated outcomes in pts who underwent definitive RT for stage I‐II FL after staging by PET‐CT. Our hypothesis was that more accurate staging will lead to better pt selection for treatment (Rx), with consequent improvement in Rx results. Methods: We conducted a multicentre retrospective study of pts who received RT for stage I‐II FL, staged by PET‐CT. Eligible pts were >=18 years with grade 1‐3A FL. Disease site, maximal bulk, and FL Prognostic Index (FLIPI) were recorded. Additional inclusion criteria were RT dose >=24Gy, follow up >=3 months, and no prior Rx. Primary outcomes were local control, freedom from progression (FFP) and overall survival (OS). Secondary outcomes were response rate by PET‐CT and toxicity.OS and FFP were estimated with Kaplan‐Meier, and uni‐ and multivariate analyses of prognostic factors performed with Cox Regression. Results: 310 pts treated from 2000‐2016 at 11 centres were eligible for analysis. Pre‐treatment characteristics included age (median 58 years, range 20‐84), female sex (n = 160, 51.6%), stage I disease (n = 254, 81.9%), FLIPI score (median 1, range 0‐3), B‐symptoms (n = 2, 0.6%), bulk of disease (median 2.5 cm, range 0.2‐10) and extranodal disease (n = 83,26.8%). Median RT dose was 30Gy (range 24‐36).Median follow up was 50 months (range 3.2‐174.6). 222/310 (71.6%) pts remain disease free. 6 pts have relapsed in field (1.9%) and 2 had marginal recurrences (0.6%). 80 pts (25.8%) relapsed at distant sites, 90.9% of all relapses.5y FFP and OS were 70.2% and 95.8%. For stage I 5y FFP was 74.3%, vs 48.1% for stage II (p < 0.0001) (Figure). There was no significant difference in 5y FFP between nodal and extranodal presentations (p = 0.23). 158 (51%) pts had a PET‐CT scan post RT. 89.9% achieved complete metabolic response (CMR) (Deauville score 1‐3). Failure to achieve CMR was associated with higher risk of progression (p = 0.03). On multivariate analysis of prognostic factors including age, stage, grade, bulk, FLIPI, RT dose, nodal versus extra nodal site, and CMR status; stage II disease (HR = 2.51, 95% CI: 1.53‐3.77, P = 0.0001) and failure to achieve CMR (HR = 3.11, 95% CI = 1.35‐7.16, P = 0.008) were significantly associated with worse FFP.Toxicity data were available on (Figure Presented) 284 pts. 67 pts (23.5%) had grade 1‐2 toxicities, with only 1 case of grade 3 toxicity (dysphagia). Conclusion: Outcome after RT in PET‐CT staged pts appears to be better than in earlier series, particularly in stage I disease, suggesting that the curative potential of RT for truly localised FL may have been underestimated.