Immune responses to malignant tumors

The immune system recognises the tumour-specific antigens (TSAs) of malignant tumours that have mutated and destroys the transformed cells. The immune system, by its network nature, acts against tumour cells by several complementary mechanisms simultaneously. In addition to TSAs, cumulative mutations can also activate silent gene sequences encoding tissue hormones, growth and differentiation factors that are no longer relevant at a given age. These tumour-specific biomolecules are called tumour-associated antigens (TAAs), or tumour markers in clinical practice. The determination of TAAs aids differential diagnosis and monitoring of therapeutic efficacy, but is not suitable for mass screening because not all tumours express TAAs and they may be produced not only in tumour lesions but also in inflammatory conditions. Usually, after a prolonged period of equilibrium, when the immune system is no longer able to destroy all tumour cells – due to increased mutations – tumour cells may escape surveillance and develop into a malignant tumour causing clinical symptoms. The aim of immunotherapies is to use immune response mechanisms to re-sensitise the malignant tumour cells to the immune functions of the invading effector.