Prognostic and predictive value of primary tumour side in patients with RAS wild-type metastatic colorectal cancer treated with chemotherapy and EGFR directed antibodies in six randomized trials.

There is increasing evidence that metastatic colorectal cancer (mCRC) is a genetically heterogeneous disease and that tumours arising from different sides of the colon (left versus right) have different clinical outcomes. Furthermore, previous analyses comparing the activity of different classes of targeted agents in patients with KRAS wild-type (wt) or RAS wt mCRC suggest that primary tumour location (side), might be both prognostic and predictive for clinical outcome.