The expression datasets of the differently expressed genes in EGC (556 upregulated gene symbols and 417 downregulated gene symbols), ERα-negative breast cancer and 4 additional cancers (small cell lung cancer, LNCaP prostate cancer cell lines, bladder cancer and Ewing sarcoma) were used in an unsupervised hierarchical clustering analysis. The gene discussed is ESR1; the disease is small cell lung carcinoma.