Abstract 5254: Postoperative adjuvant chemotherapy improves survival in stage II colon cancer? A propensity score matching analysis
Authors: Tsukamoto Ryoichi , Sugimoto Kiichi , Kawano Shingo , Niwa Koichiro , Ishiyama Shun , Kamiyama Hirohiko , Komiyama Hiromitsu , Takahashi Makoto , Kojima Yutaka , Goto Michitoshi , Tomiki Yuichi , Sakamoto Kazuhiro 
Published: July 2017

Objective : Stage II colon cancer with high-risk features have been traditionally considered more likely to benefit from postoperative adjuvant chemotherapy (POAC). National Comprehensive Cancer Network (NCCN) guidelines do not recommend routine administration of adjuvant chemotherapy for Stage II patients, except for those with high risk features, such as poorly-differentiated tumors, T4 disease, perforated tumors and those with inadequate lymph node sampling. However, the use of POAC after surgery for patients with Stage II colon cancer remains controversial. The current study was conducted to investigate the effectiveness of POAC using propensity score (PS) matching analysis, which can reduce or minimize the confounding that is seen frequently in observational studies of the effect of treatment on outcomes, based on prognostic factors.

Materials : Two hundred and nineteen patients with Stage II colon cancer who underwent surgery with curative intent between 1995 and 2005 were enrolled. The decision regarding the use of POAC was made for each case based on individual patient/physician discussions. All patients were required to provide informed consent. During the present study period, patients received 5-FU drugs orally, starting 4~8 weeks after surgery. The median observation period was 73.4 months (range: 2.2 - 184.2 months). Methods : PS matching analysis was used to adjust for differences in clinicopathological severity between the patients with and without POAC. Recurrence-free and cancer-specific survival were calculated using the Kaplan-Meier method and univariate analyses were performed using the log-rank test. The Cox proportional-hazard model was used to determine Hazard ratios and 95% confidence intervals.

Results : One hundred and nineteen patients (54.3%) underwent POAC. In univariate analysis, there were significant differences in age, invasion depth, lymphatic invasion and venous invasion between the patients with and without POAC. After PS matching analysis, in univariate analysis, there were no significant differences with respect to the clinicopathological factors between the patients with and without POAC. Before PS matching analysis significant survival benefits from POAC were not recognized for recurrence-free survival (Hazard ratio= 0.76, 95% CI 0.40-1.45, P=0.41) or cancer-specific survival (Hazard ratio= 0.52, 95% CI 0.22-1.19, P=0.12). After PS matching analysis significant survival benefits from POAC were not recognized for recurrence-free survival (Hazard ratio= 0.55, 95% CI 0.23-1.23, P=0.15) or cancer-specific survival (Hazard ratio= 0.46, 95% CI 0.16-1.18, P=0.11).

Conclusions : The one-to-one pair PS matching successfully balanced the clinicopathological factors between the patients with and without POAC. The PS matching analysis demonstrated no significant difference in survival in the patients with Stage II colon cancer.

Citation Format: Ryoichi Tsukamoto, Kiichi Sugimoto, Shingo Kawano, Koichiro Niwa, Shun Ishiyama, Hirohiko Kamiyama, Hiromitsu Komiyama, Makoto Takahashi, Yutaka Kojima, Michitoshi Goto, Yuichi Tomiki, Kazuhiro Sakamoto. Postoperative adjuvant chemotherapy improves survival in stage II colon cancer? A propensity score matching analysis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5254. doi:10.1158/1538-7445.AM2017-5254