The side of origin of colon cancer should be acknowledged as a criterion for establishing prognosis in both earlier and advanced stages of disease, experts say.

The call comes after a meta-analysis of 66 studies and more than 1.4 million patients found a 20% reduced risk of death for cancers arising on the left side.

The finding was independent of disease stage, race, adjuvant chemotherapy, year of study, number of participants, and quality of included studies, the Italian authors reported in JAMA Oncology.

 Aside from intrinsic biological differences (ie, higher rate of BRAF mutant cases) related to a more aggressive clinical behaviour, other factors might explain the worse overall prognosis for patients with right-sided cancer such as surgical technique.

“Based on the results of this study, the side of origin of CC [colon cancer] (left vs. right) should be acknowledged as a criterion for establishing prognosis in both earlier and advanced stages of disease,” the researchers said.

“Patients with right-sided tumours may deserve more aggressive treatments, especially in advanced settings and, potentially, in stage II tumours, when there are no other adverse prognostic factors.”

“Primary tumour locations….should represent an important stratification factor for future adjuvant studies,” they concluded.