We tested the association of colon tumour sidedness with prognosis and with molecular subtypes recently shown to be predictive of oxaliplatin benefit in stage III colon cancer.

NSABP/NRG C-07 trial (N=1603) was used to determine association of tumour sidedness with molecular subtypes and recurrence-free survival (RFS) and overall survival (OS).

Sidedness was associated with molecular subtypes except stem-like/CMS4 subtype. Patients with stage III, left-sided tumours showed superior OS but not RFS. Sidedness was not associated with prediction of oxaliplatin benefit when combined with 5-Fu+LV. However, greater benefit from oxaliplatin was observed in a small subset of stage III patients with left-sided, enterocyte-subtype tumours (interaction HR=0.17, P=0.01).

Sidedness was associated with molecular subtypes and was predictive of OS in stage III colon cancer but was not predictive of RFS or oxaliplatin benefit in C-07. Molecular subtypes may provide more predictive value for oxaliplatin benefit than tumour sidedness.British Journal of Cancer advance online publication, 14 December 2017; doi:10.1038/bjc.2017.448 www.bjcancer.com.