Which of the following tumor markers is classified as a tumor suppressor gene?

The classification of tumor markers is crucial in understanding their role in cancer biology. BRCA-1 is recognized as a tumor suppressor gene, which plays a significant role in maintaining genomic stability by repairing DNA breaks. When functioning properly, BRCA-1 helps prevent uncontrolled cell proliferation. Mutations in this gene can lead to an increased risk of breast and ovarian cancers, highlighting its importance as a tumor suppressor.

In contrast, carcinoembryonic antigen (CEA) and human chorionic gonadotropin (hCG) are not classified as tumor suppressor genes; instead, they are oncofetal antigens and are often elevated in specific cancers, serving primarily as markers for disease diagnosis and monitoring. Nuclear matrix protein is involved in cellular structure and organization, but it does not fit the criteria for a tumor suppressor gene in the context of cancer progression. Thus, BRCA-1 stands out as the correct answer due to its protective function against tumor development.