Colorectal cancer is the 2nd leading cause of cancer-related mortality in the United States, with a projected incidence of 153,020 new cases and 52,550 deaths in the year 2023 [1]. The most important prognostic factor for individuals with colon cancer is stage at time of diagnosis, which is determined using criteria from the 8th edition of the American Joint Commision on Cancer (AJCC) [2]. Thirty-seven percent of colon cancer patients present with early stages (1 or 2) and are considered to have disease localized to the colon, with a 5-year survival rate of 90.9 %. In comparison, patients with cancer that has spread to locoregional lymph nodes (stage 3) comprise 36 % of cases and have a 5-year survival rate of 72.8 % [3]. Stages 1–3 colon cancers will all typically undergo surgical resection with curative intent, but adjuvant chemotherapy (AC) is only recommended for stage 3 cancers, or for a subset of stage 2 cancers with a high risk of recurrence [4,5].

The identification of high-risk stage 2 colon cancer relies mostly upon a set of histopathologic features, as determined by the pathologist upon evaluation of the surgical specimen. These include higher T stage (T4), lymphovascular invasion (LVI), perineural invasion (PNI), poorly differentiated features, inadequate lymph node yield, involved margin, tumor budding, or clinical presentation with obstruction or perforation [2,4,5]. Stage 2 patients with these characteristics have been shown to benefit from AC in a number of observational studies [[6], [7], [8]].

Variations in outcomes between populations of stage 1 patients have also been observed. For example, in a study looking at patients with stage 1 colorectal cancers identified from two different national datasets from the United States, higher T stage was associated with decreased survival at 5 (T2 vs. T1 = 97.0 vs. 95.2 %) and 10 years (94.1 % vs. 90.3 %) after curative resection [9]. This effect was also seen in a German registry of 15,096 patients, in which T-stage was found to be independently associated with local recurrence (hazard ratio (HR) for T2 vs T1 = 1.82) [10]. Others have shown that expression of certain immunologic or genetic markers can correlate with adverse outcomes in stage 1 patients [6,11]. Despite these findings, risk-stratification of stage 1 patients to guide therapy is not standard practice, as it has become for stage 2 patients. This may be due, in part, to concern regarding the potential for adverse events and side effects related to chemotherapy that could offset any potential survival advantages.

During our prior work with the American College of Surgeons National Cancer Database (ACS-NCDB), we discovered a group of stage 1 colon cancer patients who according to the database had been treated with AC, in contrast to current recommendations. We hypothesized that this group of patients could represent a subset of stage 1 patients with high-risk features, similar to those used to select stage 2 patients for AC. The aim of this study was to evaluate the characteristics of this population, and to determine whether the addition of AC had any impact on survival.