Perhaps, but it is also true that these targeted therapies have different success rates among different cancers. Vemurafenib, famously approved for melanoma, hasn't been as successful in papillary thyroid.

Certainly it makes sense to consider genetic profile in treatment, but doesn't the statement "that drug should be used regardless of whether you have breast cancer or lung cancer" ignore the local tumor microenvironment and possible differences in drug resistance expression between cell types, i.e., isn't reducing cancer down to genetic profile alone potentially as problematic as reducing cancer down to its tissue of origin?

This isn't really that much of an issue because oncologists are not always idiots and can prescribe drugs off-label, with cause. Identifying a braf mutant in a disparate cancer type would probably qualify.