What is immune surveillance and how does it relate to cancer risk in immunodeficient individuals?

• A. Immune system detects and eliminates emerging neoplasms; immunodeficiency increases cancer risk due to reduced surveillance.
• B. Immune system detects only viruses.
• C. Immunodeficiency lowers risk.
• D. Immune surveillance has no relation to cancer.

Answer: (A)

Immune surveillance is the immune system constantly scanning the body's cells for abnormal changes that signal the start of cancer and destroying those transformed cells before they form tumors. Cytotoxic T cells recognize tumor-associated antigens presented by MHC molecules, while natural killer cells can detect cells with altered or reduced MHC and other stress signals. Tumor cells can sometimes evade this process by lowering antigen presentation or secreting immunosuppressive factors, but effective surveillance generally keeps cancer development in check.

When the immune system is deficient, these early detection and elimination steps are impaired, so transformed cells are more likely to grow unchecked, raising cancer risk. This is seen in conditions like HIV/AIDS, where there’s a higher incidence of certain virus-associated cancers (for example, Kaposi sarcoma and certain lymphomas), as well as other immunodeficiencies that weaken T cell or NK cell function.