In conclusion, the present study a) confirms in two independent data sets, that KCNJ3 is upregulated in breast carcinomas when compared to normal breast tissue, b) shows that increased KCNJ3 expression is significantly associated with estrogen receptor positive breast cancer subtypes, c) highlights that increased KCNJ3 is an independent prognostic marker conferring worse overall and disease free survival probabilities to estrogen receptor positive breast cancer patients, and d) demonstrates that KCNJ3 upregulation might be involved in conferring higher self-renewal capacity to cancer cells. The gene discussed is KCNJ3; the disease is cancer.