Neoadjuvant chemoradiotherapy versus neoadjuvant chemotherapy for initially unresectable locally advanced colon cancer: short-term outcomes of an open-label, single-centre, randomised, controlled, phase 3 trial.

Background: Neoadjuvant chemotherapy (NACT) is commonly used to downstage the tumor in locally advanced colon cancer (LACC) and improve the R0 resection rate. Neoadjuvant chemoradiotherapy (NACRT) is the standard treatment for locally advanced rectal and esophageal cancers, but its benefits in LACC remain poorly understood. This study aimed to compare the effects and safety of NACRT and NACT on R0 resection and survival rates in initially unresectable LACC.

Methods: This was an open-label, single-center, randomized, controlled trial conducted between May 11, 2019 and May 30, 2022. Forty-five patients with initially unresectable LACC were randomly allocated to the NACT (control, n = 20) or NACRT (research, n = 25) group. The NACT group received XELOX (oxaliplatin 100-130 mg/m², qd, d1, every 3 weeks; and capecitabine 1000 mg/m², bid, d1-d14, every 3 weeks) for 4 cycles. The NACRT group, in addition to chemotherapy, received daily irradiation (GTV 45-50 Gy/25 F; CTV 42.5-45 Gy/25 F). Surgery was scheduled 6-12 weeks after neoadjuvant treatment and adjuvant chemotherapy was administered if the patient developed resectable LACC. The primary endpoint was the 5-year overall survival (OS) rate. The secondary outcomes included the 3-year progression-free survival (PFS) and R0 resection rates. This study was registered with ClinicalTrials.gov (NCT03970694).

Findings: In short-term outcome analysis, NACRT significantly improved the R0 resection rate (80% for NACRT vs. 20% for NACT, P < 0.001). The NACRT and NACT groups had a 3-year OS of 87.6% and 75% (P = 0.037) and a 3-year PFS of 76% and 45% (P = 0.049), respectively. The 5-year OS was not reached. In the NACRT group, no local or regional recurrence was observed in patients who underwent surgery during the follow-up period, compared to two patients in the NACT group. Both NACT and NACRT were well tolerated, with no significant differences in severe adverse events. The most commonly observed grade 3-4 AE was myelosuppression (39% for NACRT and 47% for NACT, P = 0.609). No grade 5 AEs were observed between the two groups.

Interpretation: Adding radiation to NACT increased the R0 resection rate, prolonged the PFS, and potentially improved OS in selected patients with initially unresectable LACC. The trial findings indicate that this approach is safe, feasible, and may confer a survival benefit.

Funding: This study was supported by grants from the National Natural Science Foundation of China (82373213 to Dr Gao, 82202952 to Dr Wang); and the Natural Science Foundation of Guangdong Province (2023A1515010290 to Dr Chang). Funding sources were not involved in the study design, data collection, analysis and interpretation, writing of the report, or decision to submit the article for publication.