ABCG2 and breast cancer: KEGG enrichment analysis also revealed that the expanded gene families were involved in the following pathways: cytokine–cytokine receptor interaction, viral protein interaction with cytokine and cytokine receptor, chemical carcinogenesis-DNA adducts, Notch signaling pathway, and breast cancer; however, the contracted gene families were mainly involved in ABC transporters, axon guidance, antifolate resistance, antigen processing and presentation, and longevity regulating pathway-multiple pathways (Table 4).