A monumental challenge for the cure of cancer is complexity. Cancer is comprised of a heterogeneous group of diseases, classified by primary site and histologic type. Complexity of cancer is compounded by marked intertumoral heterogeneity. For example, in colorectal cancer, molecularly defined subgroups identify patients who differ in prognosis and treatment response.1 Further complexity arises from intratumoral heterogeneity and the coexistence of distinct clones.1 No wonder a one-size-fits-all approach to cancer treatment is inadequate, and precision medicine offers great promise.