It is known that the presence of BRAF mutation in mCRC predicts impaired outcome;2,4,6,33 however, these cancers are heterogeneous.9,19,20 Although the underlying mechanisms are not clarified, the present findings suggest that CA 19-9 may help identify one subgroup of BRAF-mutant mCRC patients with particularly poor prognosis. The gene discussed is BRAF; the disease is cancer.