Targeted therapies for cancers are drug treatments that target specific molecular abnormalities that are found within malignant cells and while they may be present in normal cells they are significantly more common or more important to these cancerous cells than their healthy counterparts. This term can be deceiving however, giving one the impression that the side effects of these agents are significantly less pronounced than that for their non-targeted (chemotherapeutic) counterparts; when they can be equally severe or even worse than for their non-targeted counterparts.
There are five major varieties of targeted therapies for cancers:
- Monoclonal antibodies (mAbs), which act by interfering with cell signalling (e.g., by binding to a protein signalling molecule, like, for example, VEGF-A and hence preventing it from binding to its receptors) or by triggering an immunologic response against certain cell antigens that are expressed on the malignant cells.
- Tyrosine kinase inhibitors (TKIs), which act by interfering with signalling pathways within cells by inhibiting one or more (the latter is the case for all clinically-used examples of such drugs) tyrosine kinase enzymes. These agents are often particularly helpful in treating cancers characterized by fixed molecular abnormalities that seem to contribute to their pathophysiology.
- Immunotherapies, which act by triggering or amplifying an existing immunologic response against the tumour in a way distinct from that of mAbs. Many such agents are recombinant cytokines, such as interferon alfa (IFN-α), interleukin-2 (IL-2) and tumour necrosis factor alpha (TNF-α). Other cancer immunotherapies include vaccines, which can be directed against cancer antigens or against microbial antigens; examples include intralesional BCG vaccines and cancer vaccines like sipuleucel-T and vitespen.
- Differentiation therapies (DTs), which act by inducing the differentiation of malignant cells into non-malignant functional cells. DTs include retinoids, histone deacetylase inhibitors, DNA methyltransferase inhibitors, arsenic trioxide and others.