Mutations in the BRAF gene, to name one druggable example, are a cause of many different types of cancer - melanoma, some breast, small-cell lung cancer, etc. Under the current paradigm, each type of cancer is treated as a different disease and requires a different clinical trial. This is bad.

What should happen (and is beginning to happen, with "basket trials") is that cancers are grouped by their genetic profile, instead of their tissue of origin. The BRAF V600E mutation is targetable with Vemurafenib, and so that drug should be used regardless of whether you have breast cancer or lung cancer.