Purpose: This article was designed to study the clinical outcomes and prognostic factors following radiotherapy (RT) in the multidisciplinary management of isolated retroperitoneal lymph node (RPLN) recurrence of colorectal cancer. Methods: We identified 52 patients treated consecutively with tumor-directed RT for isolated RPLN recurrence. Twenty-five patients received upfront RT (Group 1). Twenty-seven patients received RT after systemic therapy. The deferred RT was administered either to locally controlled tumors (Group 2, n = 17) or to locally progressive tumors in RPLNs (Group 3, n = 10). Results: The median overall survival and progression-free survival were 41 and 13 months, respectively, with a median follow-up time of 34 months. Survival was not significantly different among three groups. Local recurrence (32/52) was predominant and occurred earlier than distant metastasis (31/52). Two-thirds of the local recurrences (21/32) involved outfield recurrence, which was mostly in the cranial direction (15/21) from the upper margin of the RT volume. Repeated RT successfully salvaged a substantial number of patients. A shorter disease-free interval, low-dose radiation, and a tumor location above the renal vein were independent risk factors for local recurrence (all P < 0.05). A large gross tumor volume was an independent risk factor for distant metastasis (P = 0.037). No acute or late RT-related toxicity ≥ grade 3 occurred. Conclusions: Our analysis suggests that both upfront RT and deferred RT incorporated into multidisciplinary management are potentially effective treatment strategies. We found that gross tumor volume, tumor location, and disease-free interval are important prognostic factors and should be taken into consideration to decide the timing of RT.
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