Cancer marker tests, also known as tumor marker tests, are diagnostic tools used to detect specific substances in the blood, urine, or tissues that may indicate the presence of cancer. These markers are typically proteins, hormones, or other molecules produced by cancer cells or by the body in response to cancer. While not definitive for diagnosing cancer, these tests can provide valuable information about the disease's presence, progression, and response to treatment. Common cancer markers include prostate-specific antigen (PSA) for prostate cancer, cancer antigen 125 (CA-125) for ovarian cancer, and alphafetoprotein (AFP) for liver cancer and germ cell tumors. Cancer marker tests are often used in conjunction with other diagnostic methods, such as imaging studies and biopsies, to provide a comprehensive assessment of a patient's condition. They can be particularly useful for monitoring treatment effectiveness, detecting recurrence, and assessing prognosis. For instance, a rising level of a specific marker during or after treatment may suggest that the cancer is not responding to therapy or has returned. However, it is important to note that elevated levels of cancer markers can also occur in non-cancerous conditions, leading to potential false positives. Therefore, the interpretation of these tests requires careful consideration of the patient's overall clinical picture, including symptoms, medical history, and results from other diagnostic tests. In summary, cancer marker tests are valuable tools in oncology that aid in the early detection, monitoring, and management of cancer. While they are not standalone diagnostic tools, they play a crucial role in guiding treatment decisions and improving patient outcomes by providing insights into the biological behavior of tumors. As research advances, the development of new and more specific markers continues to enhance the precision of cancer diagnosis and management.