What is the difference between chemotherapy, immunotherapy, targeted therapy, and radiation therapy?
Cancer treatment modalities fundamentally differ in their mechanism of action, selectivity, and extent of coverage:
1. Chemotherapy: A systemic cytotoxic treatment that targets rapidly dividing cells and inhibits their cell cycle or DNA synthesis. Because it does not act exclusively on tumor cells, it also affects healthy, rapidly regenerating tissues, commonly causing bone marrow suppression, alopecia, and gastrointestinal symptoms as side effects.
2. Targeted therapy: A systemic treatment that inhibits specific molecular alterations, signaling pathways, or mutations responsible for tumor cell survival and proliferation (e.g., inhibition of tyrosine kinases, inhibition of oncogenic mutations using small molecules or monoclonal antibodies), thereby sparing the majority of healthy cells that do not harbor these mutations.
3. Immunotherapy: It does not directly destroy tumor cells, but rather mobilizes the body's own immune system or releases its inhibition to recognize and eradicate the tumor (e.g., anti-PD-1/PD-L1 or anti-CTLA-4 immune checkpoint inhibitors, cellular therapies).
4. Radiation therapy (Radiotherapy): Primarily a local or locoregional physical modality that utilizes ionizing radiation to induce DNA damage and direct cell death within the irradiated anatomical target area.
Chemotherapy and radiotherapy often form the backbone of multimodal treatment plans as concomitant chemoradiotherapy, whereas the use of newer-generation targeted agents and immune checkpoint inhibitors is now frequently seen in combination or sequentially to optimize locoregional and systemic control.