Maintaining clear knowledge about cancer treatments is crucial for both patients and caregivers. Two of the most widely used approaches today are chemotherapy and immunotherapy. While both aim to control and eliminate cancer, they do so through fundamentally different mechanisms. Chemotherapy, in use for several decades, targets rapidly dividing cells—both cancerous and healthy—whereas immunotherapy represents a more recent breakthrough that harnesses the body’s immune system to attack tumours naturally.This article explains how each treatment works, when they are used, their side effects, costs, and how they sometimes work together. The goal is to provide a comprehensive, up-to-date overview without any opinions—just clear facts based on current medical understanding.
How chemotherapy works and when it is used in cancer treatment
According to the Cancer Research Institute, chemotherapy uses drugs to kill cells that multiply quickly. This includes cancer cells but also healthy cells such as those in hair follicles, the gastrointestinal tract, and bone marrow. It relies on a cytotoxic effect that interferes with cell division or metabolism. Chemotherapy has historically been a first-line treatment for many cancers, including breast, lung, blood cancers, and others.Chemotherapy is administered in cycles over weeks or months, depending on the type and stage of cancer. It works systemically, meaning it can reach cancer cells throughout the body, making it useful for metastatic disease. For example, lung cancer and lymphoma are frequently treated with chemotherapy either alone or in combination with other therapies.
What is immunotherapy and where it fits in for cancer treatment
Immunotherapy does not directly attack cancer cells. Instead, it helps the immune system recognise and destroy tumours. Several forms are available today:
- Checkpoint inhibitors, which block proteins like PD-1, PD-L1, or CTLA-4, allow T-cells to attack tumours.
- CAR T‑cell therapy, including genetically modified T-cells tailored to recognise specific tumour antigens.
- Cancer vaccines are designed to stimulate an immune response against tumour-specific proteins.
- Cytokine therapy uses signalling molecules like interleukins to boost immune function.
- Oncolytic virus therapy, engineered viruses that kill cancer cells and trigger immunity.
As per Cancer Research Institute, Immunotherapy is often used for cancers known to respond well, such as melanoma, non-small cell lung cancer, bladder cancer, certain lymphomas, and gastrointestinal tumours. It can be applied in advanced or metastatic stages or, increasingly, earlier in treatment plans. Recent regulatory approvals cover multiple cancers based on biomarkers like PD-L1 expression and microsatellite instability.
Chemotherapy vs. Immunotherapy : Key differences in mechanism and effectiveness
The main distinction lies in how the treatments target cancer:
- Chemotherapy directly attacks dividing cells, regardless of whether they are malignant or not. This leads to quick tumour shrinkage but also affects healthy tissues.
- Immunotherapy engages the immune system to fight cancer more selectively. It may take longer to produce measurable results, but in some cases, it provides durable remission. Effectiveness depends on tumour type, stage, and biomarker presence.
For example, checkpoint inhibitors have shown significant long-term survival benefits in melanoma and lung cancer. However, immunotherapy is not universally effective: tumours lacking specific markers, or with low immune infiltration, may respond poorly.
Combining Chemotherapy and Immunotherapy: Synergistic benefits
Recent research shows that using both treatments together—known as chemoimmunotherapy—can improve outcomes for several hard-to-treat cancers. Chemotherapy may expose tumour antigens and modify the tumour microenvironment, making it easier for immune cells to act. Meanwhile, immunotherapy continues the attack. The combination is FDA-approved for cancers such as certain lung, head and neck, gastrointestinal cancers, and triple-negative breast cancer. Patients often experience better response rates and reduced drug resistance compared to using either therapy alone.
Side effect profiles of immunotherapy and chemotherapy: What patients should expect
Because of their different mechanisms, these treatments produce distinct side effects:
- Chemotherapy can cause hair loss, nausea, vomiting, fatigue, anaemia, immune suppression, mouth sores, nerve damage, and weight changes. These are often intense but may resolve after treatment ends.
- Immunotherapy may result in overactivation of the immune system, leading to inflammation in organs such as the lungs (pneumonitis), liver (hepatitis), colon (colitis), as well as flu-like symptoms, fatigue, skin reactions, or hormonal imbalance if endocrine glands are affected. Long-term monitoring is needed.
Response time and duration of treatment
- Chemotherapy typically involves multiple treatment cycles and shows rapid effects, with measurable tumour reduction after a few weeks.
- Immunotherapy, particularly in advanced cancers, may have a delayed onset but can provide sustained responses extending for months or years. Maintenance treatment may also continue as immune surveillance.
Immunotherapy and Chemotherapy costs and accessibility
Treatment costs vary greatly. Chemotherapy is generally less expensive, especially in resource-limited settings. In India, a full course may range between Rs 50,000 and Rs 2,00,000 per cycle. Immunotherapy, being more complex and newer, is costlier—often Rs 2,50,000 to Rs 5,00,000 per cycle in such locations. Financial assistance or insurance coverage may be available.
Effectiveness based on cancer type
The success of each treatment depends significantly on cancer type:
- Immunotherapy shows outstanding results in MSI‑High colorectal cancer, with significantly better survival compared to chemotherapy. Studies show up to a 43% reduction in mortality risk in MSI‑High patients using immunotherapy. However, effectiveness in microsatellite-stable colorectal cancer remains modest.
- Pembrolizumab, a checkpoint inhibitor, led to complete responses in 59% of certain stage 2 or 3 bowel cancer patients before surgery, versus less than 5% using traditional chemotherapy.
Patients with early-stage lung cancer treated with immunotherapy plus chemotherapy have seen survival improvements of nearly four months on average, compared to chemotherapy alone.
Chemotherapy vs. Immunotherapy: Side-by-side comparison
Understanding the differences between immunotherapy and chemotherapy is important for treatment planning. Chemotherapy remains a fast and reliable option in many cancers, while immunotherapy offers a new era of personalised treatment with potentially lasting benefits. In some cases, combining both leads to the best outcomes. Each therapy comes with its risks, costs, and suitability profile.Ultimately, treatment decisions should be made by oncologists in consultation with patients, based on cancer type, biomarkers, overall health status, and patient preferences.
