CYP2D6 and invasive breast carcinoma: CYP2D6 genotype remained the only statistically significant association with change in therapy even after adjustment for age, breast cancer type (invasive breast cancer, DCIS and lobular carcinoma in situ (LCIS)), menopausal status (pre-menopausal versus post-menopausal), report of any tamoxifen-induced side effects, previous knowledge of CYP2D6 testing, referral method (physician or nurse versus other sources) and interest in CYP2D6 testing.