Single nucleotide polymorphisms of CYP19A1 predict clinical outcomes and adverse events associated with letrozole in patients with metastatic breast cancer

The CYP19A1 gene encodes the aromatase enzyme involved in the peripheral conversion of androgen to estrogen. We evaluated the efficacy of the aromatase inhibitor letrozole in patients with metastatic breast cancer (MBC) as related to DNA polymorphisms of CYP19A1.

Among 46 SNPs examined, rs700518, rs10459592, and rs4775936 were significantly associated with higher clinical benefit rate (CBR, CR + PR + SD ≥ 6 months) (OR = 2.61 [95% CI; 1.13–6.03], P = 0.025; OR = 2.45 [95% CI; 1.06–5.65], P = 0.036; OR = 2.60 [95% CI; 1.12–6.02], P = 0.026, respectively). Median time to progression (TTP) was improved without statistical significance in patients having an over-dominant form of rs700518. In haplotype analysis, the specific haplotypes M_1_3 and M_2_1 showed a strong association with CBR (OR = 3.37 [95% CI 1.43–7.90], P = 0.005; OR = 5.33 [95% CI 1.63–17.45], P = 0.006, respectively). There was a statistically significant difference in TTP in patients with haplotype M_1_3 (5.61 months [95% CI 0.00–11.45] vs. 11.08 months [95% CI 6.75–15.42], P = 0.040) and M_2_1 (7.31 months [95% CI 4.63–9.99] vs. 12.95 months [95% CI 9.27–16.63], P = 0.038). Haplotypes M_3_5 (OR = 11.25 [95% CI 1.17–108.28], P = 0.01) and M_5_3 (OR = 4.12, [95% CI 1.09–15.61], P = 0.03) were associated with side effects of arthralgia and hot flash, respectively.