Abstract Bulky and residual tumor are considered to increase the risk of relapse in diffuse large B‐cell lymphoma (DLBCL) patients. Radiotherapy is conventionally used to reduce the risk, but the evidence is controversial. We performed a retrospective analysis to evaluate the significance of bulky and residual tumor treated with or without radiotherapy in DLBCL patients. We analyzed 312 DLBCL patients treated from 2010‐2017 in Oulu University Hospital. A bulky tumor was detected in 123 patients and 55 of these patients (44.3%) received consolidative radiation therapy (RT) to the bulky tumor. Residual tumor meeting the required criteria was found in 138 (39.3%) patients, and 65 (45.5%) of these patients received consolidative RT to the site of residual tumor. iPET‐CT scans were performed in 102 patients. In multivariate analyses, bulky was an independent risk factor in limited stage patients in progression free survival (HR 6.43 [95%CI 1.609‐25.710]; P = .008) not related to International prognostic index (HR 1.35 [95% CI 0.256‐7.124]; P = .724) or age (HR 1.62 [95% CI 0.468‐5.638]; P = .445). This was not seen in advanced stage patients or in patients with residual tumor. Radiotherapy to the bulky or residual tumor was not able to improve the long‐term PFS of patients. In this study, it appears that performing iPET is the most convincing method in improving evaluation and in finding patients with increased risk of relapse. Evidently, patients with negative iPET will not benefit from including RT in the treatment after metabolic complete response (CR), and patients with primary refractory disease are most likely in the group of positive iPET.
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