Oncologic outcomes of surgically treated colorectal cancer in octogenarians: A Comparative Study Using Inverse Probability of Treatment Weighting (IPTW)

Purpose Octogenarians constitute a growing number of diagnoses for colorectal cancer. However, the optimal treatment for these increasingly vulnerable octogenarians with colorectal cancer remains a challenging issue. The aim of this study was to evaluate the oncologic outcomes of colorectal cancer, comparing octogenarians (>80 years) and younger age (60-79 years). Methods A total of 657 patients underwent surgery for colorectal cancer between January 2015 and December 2019 at Gangneung asan hospital. Among them, 444 patients over the age of 60 were enrolled. The exclusion criteria were as follows: only local resection, R1 and R2 resection, Stage IV, absence of data in follow-up, concurrent inflammatory bowel disease, concurrent malignancy, and prior history of malignancy. The patients were divided into two groups according to their age: Octogenarian group (OG, aged > 80 years, n=83), and younger group (YG, aged 60 to 79 years, n=361). Inverse probability of treatment weight (IPTW) was used to control for confounding factors. Results We used Inverse Probability of Treatment Weighting (IPTW) to control confounding factors and ensure a balanced comparison between octogenarians (OG) and younger patients (YG). Before IPTW adjustment, the OG had significantly worse 3-year overall survival (90.0% vs. 78.6%, p=0.045), while 3-year disease-free survival (DFS) was similar between YG and OG (87.8% vs. 83.6%, p=0.349). Additionally, the OG had a higher rate of emergency surgery (21.7% vs. 11.4%, p=0.020), higher ASA classification (≥ III in 66.3% vs. 48.8%, p=0.006), higher overall mortality (43.4% vs. 21.9%, p<0.001), and less frequent use of adjuvant chemotherapy (17.2% vs. 57.6%, p<0.001). Multivariate analysis showed that older age (hazard ratio [HR] = 2.177, 95% confidence interval [CI]: 1.452-3.264, p<0.001), emergency surgery (HR = 1.831, 95% CI: 1.157-2.897, p=0.010), severe postoperative complications (Clavien-Dindo III-V. HR = 1.357, 95% CI: 1.035-1.779, p=0.027), higher TNM stage (stage III, HR = 5.143, 95% CI: 2.009-13.167, p<0.001), and presence of perineural invasion (HR = 1.588, 95% CI: 1.058-2.385, p=0.026) were significant predictors of worse survival. Similarly, independent factors associated with recurrence included emergency surgery (HR = 2.653, 95% CI: 1.550 -4.542, p<0.001), poor tumor differentiation (HR = 2.842, 95% CI: 1.198-6.743, p=0.018), higher TNM stage (stage III, HR = 7.826, 95% CI: 2.355-26.016, p<0.001), and presence of perineural invasion (HR = 1.876, 95% CI: 1.152-3.055, p=0.011). However, age was not an independent factor associated with recurrence. In the subgroup analysis, the OG group with no or mild complications (Clavien-Dindo classification I-II) had a significantly better 3-year OS compared to those with severe complications (87.7% vs. 37.5%, p=0.002). After IPTW adjustment, there were no significant differences in OS (73.2% vs. 77.5%, p=0.120) or DFS (87.2% vs. 87.5%, p=0.863) between the two groups. These findings suggest that age alone is not a critical determinant of oncologic outcomes once confounding variables are controlled. Conclusion After IPTW adjustment, age was not an independent factor affecting oncologic outcomes. Instead, emergency surgery, severe complications, advanced stage, tumor differentiation, and perineural invasion were significant predictors of survival and recurrence. In the subgroup analysis, octogenarians with no or mild complications had significantly better 3-year OS than those with severe complications. These findings suggest that perioperative management and disease severity, rather than age alone, should guide treatment decisions.