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The management of lateral pelvic lymph nodes (LPLN) in locally advanced rectal cancer is controversial, with limited data indicating if prophylactic resection or neoadjuvant therapy results in improved outcomes. There are no data regarding the management of LPLN in the setting of short course radiation (SCRT) with non-operative management. We evaluate a novel, definitive approach to addressing LPLN incorporating a simultaneous integrated boost to manage clinically suspicious LPLNs in patients receiving SCRT followed by chemotherapy (SCRT-CH) in a non-operative management paradigm.

Patients with locally advanced rectal adenocarcinoma who were treated with SCRT-CH with non-operative intent were included. All primary tumors were biopsy confirmed and disease staged with pelvic MRI. SCRT was delivered to the pelvis using intensity modulated RT to a dose of 25Gy in 5 daily fractions with a simultaneous integrated boost to 35Gy in 5 fractions to clinically enlarged, radiographically suspicious LPLNs. Patients then underwent consolidation chemotherapy with the goal of using mFOLFOX. Patients with clinical partial response (cPR) to SCRT-CH underwent total mesorectal excision (TME). No patients underwent lateral pelvic nodal dissection at time of TME. Progression free survival (PFS), distant metastasis free survival (DMFS), overall survival (OS), and local failure free survival (LFFS), including primary site and boosted LPLN nodal failures, were assessed.

Between June 2017 and January 2021, 30 patients were treated with non-operative intent. Median follow-up from completion of SCRT was 24 months. 40% of patients were female with median age at diagnosis of 59 years. 90% of patients were ECOG 1 or less. 60% of tumors were low lying rectal (0-5cm from the anal verge), 33% middle (5-10cm), and 7% high (10+ cm). Stage breakdown included 7% stage II, 83% stage III, and 10% stage IVA and 14 patients had involvement of the circumferential resection margin on initial staging. 80% of patients received at least 8 cycles of consolidation chemotherapy with the vast majority (93%) of patients receiving mFOLFOX and the remaining patients (7%) receiving CAPOX. 12 patients (40%) had a cPR and underwent surgery with 50% receiving APR and 50% receiving LAR. Mean OS was 35 months (95% CI 29.0-40.3 months) with 1 and 2-year OS at 82.7% and 71%, respectively. PFS at 1 and 2 years were 76% and 58%, respectively. DMFS at 1 and 2 years was 100% and 80%, respectively. Two patients (7%) developed failures at the site of boosted LPLNs. Six patients (20%) developed a local regrowth at rectal primary site, 5 which were receiving non-operative management. The LFFS at 1 and 2 years of 86% and 77%, respectively.

These early data indicate that LPLN management with a simultaneous integrated boost in the setting of SCRT-CH with non-operative intent may result in effective loco-regional control in patients with locally advanced rectal cancer.