What Is Immunotherapy — And How Does It Actually Fight Cancer?

The immune system is already in the business of finding and destroying abnormal cells. Cancer is, in part, a failure of that system — tumour cells develop ways to hide from immune surveillance, to send "don't attack me" signals that healthy cells would never need to send. Immunotherapy is the attempt to undo that evasion.

It is not chemotherapy. Chemotherapy poisons rapidly dividing cells — cancer cells, yes, but also hair follicles, gut lining, bone marrow. Immunotherapy works differently. It tries to teach the immune system to recognise the tumour as the threat it is, and then get out of the way.

The Main Types of Immunotherapy

1. Checkpoint Inhibitors

This is the class most people mean when they say "immunotherapy." The tumour uses checkpoint proteins — specifically PD-L1, CTLA-4, and similar molecules — as a kind of camouflage. The cancer cell waves these signals at passing immune cells, essentially saying: "Nothing to see here. Don't attack." Checkpoint inhibitor drugs block this interaction. Once the signal is jammed, the immune system's T cells can recognise and kill the cancer cell.

Pembrolizumab (Keytruda) and nivolumab (Opdivo) are PD-1 inhibitors. Atezolizumab targets PD-L1 directly. Ipilimumab targets CTLA-4. These drugs have produced remarkable results in some patients — not all — with lung cancer, melanoma, bladder cancer, and several other types.

The critical detail: tumour PD-L1 expression and microsatellite instability (MSI) status determine whether a patient is likely to respond. Testing for these before prescribing immunotherapy is standard practice at India's accredited oncology centres.

2. CAR T-Cell Therapy

This is more complex and more targeted. T cells are taken from the patient's blood, genetically engineered in a lab to express chimeric antigen receptors (CARs) that recognise specific proteins on the surface of cancer cells, and then reinfused in large numbers. These modified T cells hunt down and kill cells bearing that specific antigen.

CAR T-cell therapy has produced striking complete remissions in patients with certain blood cancers — particularly B-cell lymphoma and acute lymphoblastic leukaemia — who had failed multiple prior treatments. It is not yet widely available but is offered at select Indian centres including those in the network Prime Medical Solutions works with.

3. Monoclonal Antibodies

Antibodies that target specific proteins on cancer cells. Trastuzumab (Herceptin) targets HER2-positive breast and gastric cancer. Rituximab targets CD20 on B-cell lymphomas. Cetuximab targets EGFR in colorectal and head and neck cancers. These are sometimes called targeted therapy rather than immunotherapy, depending on classification, but the mechanism uses the immune machinery.

4. Cancer Vaccines

Therapeutic vaccines designed to stimulate immune response against tumour-specific antigens. Sipuleucel-T for prostate cancer is the established example. Cancer vaccine research is an active area with several candidates in clinical trials.

5. Cytokines

Interleukins and interferons that boost immune activity generally. High-dose interleukin-2 for melanoma and kidney cancer was one of the earlier immunotherapy approaches. Less used now that checkpoint inhibitors have shown stronger and more predictable responses.

Who Actually Responds to Immunotherapy

This is the honest part that gets glossed over in headlines. Immunotherapy works dramatically for some patients and not at all for others. The factors that predict response:

1. PD-L1 expression. High PD-L1 on the tumour surface generally predicts better response to PD-1/PD-L1 inhibitors. But it is not absolute — some PD-L1-low patients respond, some PD-L1-high patients do not.

2. Tumour mutational burden (TMB). Tumours with many mutations tend to produce more abnormal proteins the immune system can recognise. High TMB is associated with better checkpoint inhibitor responses across cancer types.

3. Microsatellite instability (MSI-H) / mismatch repair deficiency (dMMR). These cancers — regardless of where they started — respond well to pembrolizumab. This was the basis for the first tumour-agnostic cancer drug approval.

4. Specific cancer types. Melanoma and lung cancer have shown strong responses. Some other cancers — pancreatic cancer, most glioblastomas — have been largely resistant to checkpoint inhibitors so far.

Side Effects — Not as Mild as the Headlines Suggest

Immunotherapy does not cause hair loss and the severe nausea of chemotherapy. But it has its own serious toxicities, because activating the immune system too broadly can damage healthy tissues.

Immune-related adverse events (irAEs) include colitis, pneumonitis, hepatitis, endocrine gland inflammation (thyroid, pituitary, adrenal), and skin reactions. Some are managed easily with steroids. Some are severe and require stopping treatment. Deaths from irAEs, while uncommon, occur. Patients receiving immunotherapy need monitoring by experienced oncology teams who know what to look for.

Immunotherapy in India — What Is Available

India's accredited oncology centres — including those in the Prime Medical Solutions network — prescribe and administer all major checkpoint inhibitors. Pembrolizumab, nivolumab, atezolizumab, and ipilimumab are available. Generic versions of some agents have entered the Indian market, which reduces cost considerably for long treatment courses.

Dr. Rakesh Jalali at Apollo Proton Cancer Centre, Chennai — Medical Director and Lead of Neuro Oncology — is among the oncologists in Prime Medical's network who manages patients with complex cancer presentations including immunotherapy-eligible cases. Dr. Rohit Nayyar at Max Super Speciality Hospital, Saket, Delhi handles cancer care including immunotherapy coordination for international patients. Dr. Niti Raizada and Dr. Saratchandra Pingali at Fortis Hospital, BG Road, Bengaluru also manage immunotherapy cases for African and international patients.

Molecular testing — PD-L1, TMB, MSI status, next-generation sequencing — is available at the hospitals Prime Medical works with. For African patients who receive a cancer diagnosis at home without this testing, the molecular workup can be completed on arrival in India before treatment starts.

The Question Worth Asking

If you or a family member has been diagnosed with cancer and a doctor has mentioned immunotherapy, the most important first step is confirming which specific drugs are being considered, what the biomarker testing showed, and why immunotherapy is being recommended for this particular tumour type and stage.

India's oncologists at Prime Medical's partner hospitals review cases remotely — share the biopsy report, imaging, and any molecular testing already done, and receive a written specialist opinion within 48 hours.

To book a consultation, call the number on our website.