Clinicopathological characteristics and impact on efficacy of three versus six months of adjuvant chemotherapy in early-onset colon cancer: ACHIEVE and ACHIEVE-2 trials

60 Background: Colorectal cancer (CRC) incidence and mortality have decreased since the 1970s but several data such as the SEER CRC registry show that the incidence of early onset colon cancer (eoCC, age 20-49) and RC keep increasing. There is limited results suggesting eoCC may have different behaviors compared to traditional CC (tCC, age ≥ 50). Methods: Individual patient data of 1,805 high-risk stage II/III colon cancer (CC) patients (pts) as the modified ITT population in ACHIEVE and ACHIEVE-2 trials were investigated. Clinicopathological features and treatment-related data were assessed by age group. Disease-free survival (DFS) was assessed by Kaplan-Meier curves and Cox multivariable models adjusted by trials, regimen, T and N. Results: Of the 1,805 pts, eoCC were 155 pts (8.6%). Using 5% difference between age groups as clinically meaningful cutoff, eoCC had similar gender (female, 52 vs 48%), PS (PS = 1, 1 vs 4%), risk group (high-risk, 43 vs 42%) and T stage (T4, 30 vs 30%) as tCC, while eoCC were less likely right-sided colon primary (32 vs 39%), had N1 disease (48 vs 54%), and treated by FOLFOX (16 vs 23%). Overall, eoCC significantly had a worse DFS than tCC (3y-DFS, 75 vs 82%; Adjusted Hazard Ratio = 1.40: 95% Confidence Interval, 1.00-1.95: p= 0.0478); in addition, similar DFS were observed among tCC pts (age 50-69 vs >70). eoCC experienced less neutropenia, thrombocytopenia and stomatitis, but had more diarrhea, nausea and/or vomiting. There were 38 and 297 pts with an initial relapse in eoCC and tCC, respectively. Of those, peritoneal metastases were more frequently seen in eoCC (n = 13, 34%) than in tCC (n = 63, 21%) (p = 0.097), whereas liver and lung metastases were similar between the two groups. Impact on DFS of 3 versus 6 months of adjuvant chemotherapy in eoCC (3y-DFS, 75% vs 76%) is similar to that in tCC (83% vs 81%). Conclusions: eoCC had unique characteristics; the difference in DFS between eoCC and tCC were potentially due to a different metastatic spread. eoCC had a different adverse event profile compared to tCC. No impact on DFS of treatment duration in eoCC was suggested. Clinical trial information: UMIN000013036.