Lindstrom and coworkers have explored the spatial tissutal distribution of ER in tumor biopsies of 1780 postmenopausal breast cancer patients randomly assigned to receive or not adjuvant tamoxifen and have classified the samples into two groups: low intratumor heterogeneity and high intratumor heterogeneity; patients with high intratumor heterogeneity of ER had a two-fold increased long-term risk as compared with patients with low intratumor heterogeneity [265]. The gene discussed is ESR1; the disease is breast carcinoma.