Our results showed that CYP2D6 polymorphisms associates significantly with Her-2 –amplification, as it was present in 60% of the refractory group, and in all responding patients with mutant CYP2D6. Even though it was not in agreement with Okishiro (2009), who reported no significant association detected between CYP2D6 polymorphisms and Her-2 –amplification in the Japanese BC patients. The gene discussed is CYP2D6; the disease is breast cancer.