A new prognostic and predictive tool for shared decision making in stage III colon cancer.

Background: Survival of patients with stage III colon cancer varies widely according to T-N sub-stages. Estimating the benefit of each therapeutic option in each T-N subgroup may provide more accurate information helping doctors and patients in the complex shared decision-making process surrounding adjuvant therapy.

Methods: The outcomes data of 12,834 patients with stage III colon cancer enrolled in the IDEA trial served as our database. Patients were categorised in 16 sub-stages, based on T-N categories. We created a meta-regression model to predict the expected 5-year DFS within each T-N sub-stage. We then evaluated the efficacy of each therapeutic option in every sub-stage, working backward by subtraction, using an average of the HRs reported in pertinent trial publications as a conversion factor.

Results: Large differences in 5-year DFS rate were observed among the subgroups, ranging from 89% (T1N1a) to 31% (T4N2b) in the overall population. The contribution to the outcome of each therapeutic option in this setting varied widely across sub-stages. According to our model, patients with T1N1a cancers have a projected 5-year DFS of 79.6% with surgery alone. Adjuvant fluoropyrimidine alone results in 5.6% absolute DFS gain; an additional 2.3% and 0.8% gain is seen with oxaliplatin for 3 and 6 months, respectively. Patients with T4N2b cancers show a 13.9% 5-year DFS with surgery alone, and an 11.2%, 6.4%, 2.5% increase with the aforementioned adjuvant options, respectively.

Conclusion: The resulting overlay bar graph gives patients and doctors the projected relative benefit of each treatment option and may substantially help the shared decision-making process, although caution must be exercised in using this model due to the significant variance of the estimates.