The basic model adjusted for age and race showed a statistically significant association between higher radon exposure and risk of ER−/PR- breast cancer (p for trend = 0.01) and ER−/PR−/HER2- breast cancer (p for trend = 0.003) and a suggestive association for risk of ER- breast cancer (p for trend = 0.06). The gene discussed is ERBB2; the disease is breast carcinoma.