Tumour markers, also known as biomarkers, might be proteins, conjugated proteins, peptides, or carbohydrates. Tumour markers are substances that are created by cancer cells or by the organism in response to cancer. According to the dictionary of cancer terms published online by the National Cancer Institute (NCI), a biomarker is "A biological molecule found in blood, other body fluids, or tissues that is a sign of a normal or abnormal process, or of a condition or disease." These molecules are present in the blood, urine, tissues, and body fluids (cerebrospinal fluid, synovial fluid, pancreatic fluid, etc.). However, blood levels are primarily examined. Tumour markers are never utilized to make a cancer diagnosis. Mammography, ultrasound, computed tomography, magnetic resonance imaging scans, and tumour marker assays are used to aid in the diagnosis, monitor the progression of the disease (prognosis), detect recurrence, and aid in the application of treatment. While these procedures are beneficial for staging cancer, a biopsy is usually required to confirm the diagnosis. Considering tumour markers is an exciting field for both veterinary oncology and human medicine, the purpose of this study is to provide current and relevant information for the future use of tumour markers for the diagnosis and prognosis of increasing cancer cases in animals by reviewing previous studies.