The IHC HER2, ER, PR, and PDL-1 staining test involves assessing protein expression levels in breast and other cancers using immunohistochemistry (IHC) staining. Tumor issue sections are reacted with specific antibodies against cellular protein antigens, stained, examined under a microscope, and interpreted. This study provides details about cancer subtypes, planning for targeted oncology therapies, predicting responses to immunotherapy, and the prognostication of cancer.