Genetic and transcriptomic analyses of early-onset colon cancer (EOCC): a post hoc analysis of 2973 patients from two adjuvant randomized trials

Background

Despite decreasing colon cancer (CC) incidence worldwide, an inverse trend is being registered since the late 1990s in people <50 years old, possibly due to an increasing exposure to lifestyle-related risk factors/exposome. Early-onset CC (EOCC) typically manifests in more advanced stages and may harbor a distinct genetic profile. However, its prognosis remains controversial, and disease stratification through gene expression-based subtyping could potentially provide insight.

Materials and methods

We collected data from stage III CC patients enrolled in PETACC-8 and IDEA-France and we analyzed them according to a cut-off of 50 years of age, defining EOCC and late-onset CC (LOCC). Molecular analyses were carried out to evaluate mismatch repair deficiency (dMMR) and extended genetic profile. RNA-sequencing analyses were carried out to determine consensus molecular subtypes (CMS).

Results

A total of 2607 LOCC and 366 EOCC were included. When compared to LOCC, EOCC were in better general conditions and presented more advanced-stage diseases. EOCC were more often dMMR, CMS1, RAS wild-type, and mutated for PTEN, CTNNB1, ERBB2, and DDR2. Relapse-free survival (RFS) was similar in the two age groups (3-year rate 74% versus 76%), but differences were observed according to CMS. In CMS1, a better RFS was observed in mismatch repair-proficient (pMMR) EOCC versus LOCC (3-year rate 82% versus 63%, P = 0.041), while this was not observed in dMMR CMS1.

Conclusions

In conclusion, EOCCs are diagnosed in more advanced stages, are more often dMMR, harbor a specific genetic profile, and have similar RFS when compared to LOCC, even if the age effect on RFS appeared to vary among CMS groups.