Biomarkers in cancer are biological indicators that can be measured to assess the presence or progression of the disease. They can be molecules found in blood, other body fluids, or tissues, and may include proteins, genes, or specific cellular changes. Biomarkers help in diagnosing cancer, predicting its behavior, and determining the best treatment options. These indicators can also monitor how well a treatment is working or if the cancer is returning. Examples of cancer biomarkers include HER2 for breast cancer and PSA for prostate cancer. Understanding these biomarkers is crucial for personalized medicine and improving patient outcomes.