PURPOSE/OBJECTIVE(S): We previously reported 30% of patients with localized follicular lymphoma (FL) staged by 18F-FDG-PET-CT (PET-CT) receiving primary radiotherapy (RT) will relapse within 5 years. We sought to report outcomes for those who relapsed.MATERIALS/METHODS: We conducted a multicenter retrospective study of patients who received RT=24Gy for stage I-II FL grade 1-3A FL, with age=18 years, and PET-CT staging. Observation was defined as >6 months without treatment from relapse. Overall survival (OS) and freedom from progression (FFP) were estimated with Kaplan-Meier, and uni- and multivariable analyses (MVA) with Cox regression.RESULTS: Of 512 patients with median follow up of 52 months, 149 (29.1%) developed recurrent lymphoma at a median 23 months (range, 1-143) after primary RT. Median follow up was 33 months post relapse. 3-year OS was 91.4% after recurrence. OS was significantly worse for those with relapse =12 months from date of diagnosis versus all others, 88.7% versus 95.8%, respectively (p=0.01), and remained significantly worse on MVA (FLIPI-adjusted HR=3.61, p=0.009). Histology at relapse included: 93 indolent (grade 1-3A), 3 FL grade 3B/NOS, 18 diffuse large B-cell lymphoma (DLBCL); 35 patients were not biopsied. Of those with follow up =3 months and biopsied (n=74) or presumed (n=23) indolent recurrence, 58 patients (59.8%) were observed, 19 (19.6%) had systemic therapy, 16 (16.5%) RT, and 4 (4.1%) systemic therapy+RT. For patients with indolent recurrences that were observed, 3-year FFP or freedom from treatment was 56.6% (median, 48 months). For all patients with biopsied/presumed indolent recurrence receiving salvage treatment (n=59, including 20 initially observed) 3-year FFP was 73.9%.CONCLUSIONS: Prognosis for patients with relapsed FL following primary radiotherapy is excellent supporting the role of primary radiation in the management of early stage disease. Patients with localized FL treated with primary RT who experience early relapse (<12 months) have inferior survival to those with longer disease-free interval.
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