Biological Therapy — Harnessing Living Systems to Fight Cancer

Biological therapies represent a broad category of oncology treatments that harness biological mechanisms rather than relying purely on cytotoxic synthetic chemicals. The category includes monoclonal antibodies, immune checkpoint inhibitors, cancer vaccines, adoptive cellular therapies (such as CAR T-cell therapy), cytokines, and oncolytic viruses.

Mechanistically, these therapies work along several pathways. Some flag cancer cells so that endogenous cytotoxic T cells and natural killer cells can recognise and destroy them. Others alter the tumour microenvironment, block growth factor signalling, prevent tumour neo-angiogenesis, or deliver targeted payloads directly to malignant cells while sparing healthy tissues to a greater extent than traditional chemotherapy.

The introduction of biological therapies has transformed outcomes across many cancers that historically responded poorly to standard cytotoxic regimens. For patients, these agents often provide durable disease control and, in some cases, long-lasting remissions. Because their mechanisms differ from traditional chemotherapy, their side-effect profiles are distinct, requiring specialist monitoring for immune-mediated reactions, skin toxicities, or systemic inflammatory responses.

Suitability for biological therapy relies heavily on biomarker profiling. Tests include immunohistochemistry to measure PD-L1 expression, next-generation sequencing for microsatellite instability (MSI-H) or tumour mutational burden (TMB), and fluorescence in situ hybridisation (FISH) for gene amplifications such as HER2. Blood tests also monitor cytokine release and inflammatory markers during treatment.

Biological therapies are approved across numerous malignancies, including malignant melanoma, non-small cell lung cancer, renal cell carcinoma, colorectal cancer, and haematological malignancies like leukaemia and lymphoma. Monoclonal antibodies are widely used in HER2-positive breast cancer, and checkpoint inhibitors play a central role in bladder and head and neck cancers.

Biological therapies are administered intravenously, subcutaneously, or orally, frequently in combination with chemotherapy, surgery, or radiotherapy. They may be given as first-line treatment, adjuvant therapy to prevent recurrence, or maintenance therapy. Toxicities include immune-related adverse events, such as pneumonitis, colitis, or thyroiditis, which require prompt management with corticosteroids or immunosuppressive drugs.