Nowadays breast cancer is the most often diagnosed life-threatening cancer in women. It is the leading cause of cancer death among women, accounting for 23% of the total cancer cases and 14% of the cancer death. MCF-7 is a commonly used breast cancer cell line that has been promoted for more than 40 years by multiple research groups Breast cancer is diagnosed using microarray technology. Microarray technology is a powerful technique used to compare differences in gene expression between mRNA samples. Comparing RNA prepared from breast cancer cells and normal cells can lead to the identification of sets of genes that play a key role in disease. The genes that are responsible to cause cancer is identified using GEO2R. GEO2R is the web tool used to compare two or more samples and identify a gene that shows differential expression. There are three comparisons, the comparison is between the expression pattern of 17b-estradiol responsive genes, OHT-resistant, and ICI-resistant in MCF-7 breast cancer cell line. The comparison between all the sets are done by Venny 2.0. to identify the common genes and the gene ontology is studied.