Estrogen receptor status in CHEK2-positive breast cancers: implications for chemoprevention

To investigate the relationship between CHEK2 mutation status and estrogen receptor (ER) status in unselected cases of early-onset breast cancer from Poland, we screened 4441 women diagnosed with breast cancer younger than 51 years and 7217 controls for three inherited mutations in CHEK2 (1100delC, IVS2+1G>A, del5395). ER status was compared between CHEK2 -positive and CHEK2 -negative breast cancer cases. A truncating mutation in CHEK2 was seen in 140 of 4441 cases and in 70 of 7217 controls [odds ratio (OR) = 3.3; 95% CI = 2.5–4.4; p < 0.0001]. ER status was available for 92 of 140 mutation carriers and for 3001 of 4301 non-carriers with breast cancer. The OR was higher for ER-positive cancers (OR = 3.9; 95% CI = 2.7–5.4; p < 0.0001) than for ER-negative cancers (OR = 2.1; 95% CI = 1.3–3.3; p = 0.002). Sixty-six of the 92 breast cancers in carriers of CHEK2 truncating mutations were ER positive compared with 1742 of the 3001 breast cancers in non-carriers (72% vs 58%; p = 0.01). Women with a CHEK2 mutation face a fourfold increase in the risk of ER-positive breast cancer and might be candidates for tamoxifen chemoprevention.