What is the purpose of tumor markers in oncology?

The purpose of tumor markers in oncology mainly focuses on monitoring treatment efficacy and assessing prognosis. Tumor markers are substances, often proteins, that are produced by cancer cells or by the body in response to cancer. When a patient is diagnosed with cancer, measuring levels of these markers can help physicians to evaluate how well a treatment is working, as an increase or decrease in marker levels can indicate whether the cancer is responding to therapy or worsening. Additionally, certain tumor markers can offer information regarding the likely progression of the disease, helping healthcare professionals to stratify patients based on their prognosis.

The other options do not accurately reflect the role of tumor markers. Tumor markers do not have any influence on tumor size directly, nor do they provide a cure for cancer or eliminate the need for chemotherapy. Their main utility lies in the monitoring and prognostic assessment, which aids in making informed decisions regarding a patient's course of treatment.