Because of increasing evidence that specific somatic tumor mutations are both prognostic (e.g. ESR1 [2–4]) and predictive in MBC (e.g. ESR1 [3] and PIK3CA [4–6]), somatic genomic testing has become standard of care and offers great promise in the advancement of novel therapeutics and precision cancer medicine [7–10]. The gene discussed is ESR1; the disease is cancer.