The proteins with regulated ubiquitylation levels – NADPH-cytochrome P450 reductase, bifunctional 3′-phosphoadenosine 5′-phosphosulfate synthase 1, ATP-binding cassette sub-family E member 1, and fatty acid synthase – could have functional implications in the differentiation between the breast cancer subtypes used for this study. The gene discussed is PAPSS1; the disease is breast cancer.