Immunotherapy — Treatments Harnessing the Immune System

Immunotherapy encompasses several therapeutic approaches designed to overcome the mechanisms tumours use to evade immune surveillance. Normal immune cells use biochemical checkpoints to avoid attacking healthy tissues. Cancer cells frequently exploit these pathways by producing signals that turn immune cells off, effectively hiding in plain sight. Checkpoint inhibitors disrupt this disguise by blocking inhibitory proteins, restoring the immune system's capacity to attack the tumour.

Other forms of immunotherapy include chimeric antigen receptor (CAR) T-cell therapy, where patient T cells are genetically re-engineered to seek out cancer cells, as well as therapeutic cancer vaccines and monoclonal antibodies. These therapies stimulate diverse elements of the immune system, either non-specifically or by directing cells toward defined tumour antigens.

Immunotherapy has reshaped cancer care by providing effective treatment options for advanced diseases that previously had few solutions. One defining feature of successful immunotherapy is the potential for long-lasting responses, as the immune system can 'remember' cancer cells long after treatment finishes. However, because it stimulates immune activity, it can also cause the immune system to attack normal tissues, leading to unique inflammatory side effects. Understanding immunotherapy helps patients identify symptoms early and work closely with their healthcare team.

Eligibility is often determined using predictive biomarkers measured via immunohistochemistry or genomic sequencing. Key tests include PD-L1 expression, microsatellite instability (MSI-H) or mismatch repair deficiency (dMMR), and tumour mutational burden (TMB-High).

Immunotherapy is approved to treat many cancers, including melanoma, non-small cell lung cancer, renal cell carcinoma, bladder cancer, Hodgkin lymphoma, head and neck cancers, triple-negative breast cancer, and tumours exhibiting mismatch repair deficiency or microsatellite instability regardless of their primary site.

Immunotherapies are given as intravenous infusions, subcutaneous injections, or cellular infusions. They may be prescribed alone or combined with chemotherapy, targeted therapy, or radiation. Managing immune-related adverse events, such as colitis or pneumonitis, often requires prompt treatment with corticosteroids.