How Targeted Therapy and Immunotherapy Work

How targeted therapy works

These two drug classes are so often mentioned in the same breath that many people assume they are the same thing. They are not. Targeted therapy and immunotherapy work through entirely different mechanisms, are guided by different biomarkers, and produce very different side effects. This article, prepared by the YOUNIFY Clinic medical team, explains both in plain language so that you can have a more precise conversation with the oncologist who is treating you.

Targeted therapy acts on a specific molecule or signalling mechanism identified in the tumour, rather than broadly on rapidly dividing cells throughout the body. That is why a biomarker result must support it before it is used; it cannot be selected from the cancer type alone. The report that carries those results is described in comprehensive genomic profiling.

A simple analogy: some cancer cells have a switch stuck in the on position, so the cell keeps receiving a signal to grow and divide. That switch usually comes from an alteration in a particular gene, and a targeted drug interrupts the signal from that switch specifically.

The class includes several forms, the most common being:

• Oral tyrosine kinase inhibitors (oral TKIs) — small-molecule tablets that block signalling inside the cell, typically used where alterations involving EGFR, ALK, ROS1, RET, MET, BRAF or NTRK are found in an appropriate disease context.
• Antibody-based agents — proteins designed to bind a receptor on the tumour cell surface, for example where HER2 amplification is identified in a suitable setting.
• Agents directed at the tumour's DNA repair machinery — used where a defect in that machinery has been demonstrated.

The principle is simply that a target must exist before a matched drug can. If testing finds no target, there is no rationale for using this class, and not every tumour carries a genomic alteration for which a targeted drug exists.

How immunotherapy works

Immunotherapy does not act on the tumour cell directly. It adjusts the patient's own immune system so that it recognises and deals with the tumour more effectively. The class most widely used today acts on immune checkpoints.

The immune system has natural brakes so that it does not damage the body's healthy cells. These brakes are called immune checkpoints, and some tumours exploit them to avoid detection. Immune checkpoint inhibitors ease those brakes so that T cells can function more normally. The checkpoints most often discussed are the PD-1/PD-L1 axis and CTLA-4.

The biomarkers used to inform this decision include PD-L1 (how much of the protein is expressed), MSI (instability in repeated genetic sequences) and TMB (the overall mutation burden in the tumour). None of them predicts perfectly: someone with a favourable value may not respond, and the reverse also happens.

The checkpoint agents in current use are given intravenously, so they are administered under medical supervision with a monitoring system in place.

One point is worth stating plainly for readers researching options from abroad: these biomarker tests are ordered for people who already have a cancer diagnosis. They are not a cancer screening test for people who do not.

Chemotherapy, targeted therapy and immunotherapy compared

The table below sets out how the three approaches patients most often hear about differ. Each answers a different question, and none is generally superior to the others; the choice depends on the disease type and stage, the biomarker results and the person's overall condition. For the wider framework, see what precision oncology is.

At YOUNIFY, chemotherapy, radiotherapy and cancer surgery are arranged through coordinated referral to a partner facility. What the clinic itself handles is diagnostic imaging, tumour genomic testing, multidisciplinary review, and treatment with targeted therapy and immunotherapy.

Side effects to watch, and when to call the team

Both classes have side effects that require active monitoring, and their character differs clearly from chemotherapy. Knowing in advance which symptoms to report quickly is part of treating safely — particularly if you travel home between cycles.

With targeted therapy, the common effects tend to involve the skin and gut: an acne-like rash, dry skin, nail inflammation, diarrhoea, mouth soreness. Some people see changes in liver values or a rise in blood pressure. Most are managed with supportive care and dose adjustment by the medical team. The symptom to report immediately is new breathlessness or a new dry cough, which can relate to inflammation of lung tissue — uncommon, but important.

With immunotherapy, side effects arise because the immune system becomes overactive against healthy organs (immune-related adverse events). The organs most often involved are the thyroid, skin, bowel, liver and lungs. These can appear early in treatment or some time after it has stopped, so periodic blood tests and symptom review are part of the plan. Report promptly: increasing diarrhoea or blood in the stool, a spreading rash, unusual fatigue, breathlessness, or yellowing of the eyes or skin.

Managing these effects belongs with the medical team. Please do not self-medicate or stop treatment on your own when symptoms appear.

If you are being treated in one country and monitored in another, agree the handover explicitly before you travel: which blood tests, at what interval, who reads them, and how a result outside the expected range reaches the physician responsible for your treatment.

• New breathlessness, or a new dry cough
• Diarrhoea that is getting worse, unusually frequent stools, or blood in the stool
• A rash that spreads quickly, blisters, or sores in the mouth or other linings
• Yellowing of the eyes or skin, or dark urine
• Unusual fatigue, palpitations, rapid weight change, or other symptoms that may relate to the thyroid
• Fever with no clear cause, or any new symptom that keeps worsening between appointments

Who these treatments may suit

In general, whether either class is considered depends on the biomarker results, the disease type and stage, prior treatment, overall condition and comorbidities — not on patient preference alone.

• People with a genomic alteration matched by a drug that acts on it, in an appropriate disease context.
• People whose immune-side biomarkers support consideration of immunotherapy, with no significant contraindication.
• People whose disease has progressed on current treatment and for whom new molecular information opens an additional option.
• People whose overall condition suits the treatment and who can attend the follow-up it requires.

Groups needing special consideration, or for whom these may not be appropriate, include people with no matched target or supporting biomarker, people with active autoimmune disease, transplant recipients, people on high-dose immunosuppression, people with liver or kidney function limits, and people on long medication lists where interactions are likely. These situations are assessed individually by the medical team.

Limitations you should know

Both classes represent meaningful progress in cancer care, but they carry limits worth understanding from the start so that expectations match what the drugs can actually do.

• Not every tumour carries a genomic alteration for which a targeted drug exists, so a proportion of patients simply have no indication for targeted therapy.
• Even where a matched target is found, no one can say in advance whether a given person will respond. Outcomes vary from person to person.
• Resistance commonly emerges over time as the tumour adapts, which is why monitoring continues and repeat testing — from tissue or from blood — may be discussed. See liquid biopsy and ctDNA testing.
• Immune-side biomarkers are imperfect predictors; a favourable value does not assure a response, and an unfavourable one does not exclude it.
• Both classes need systematic side-effect surveillance, and some symptoms need attention quickly.
• They do not replace standard treatment in every situation; in many cases they are used alongside or after other treatment.
• Please decide together with the physician who is treating you, do not adjust or stop your current treatment on your own, and do not change medication based on something read online without discussing it first.

Costs depend on which tests and which plan are involved. The medical team assesses and explains all costs before anything begins.

What to expect at YOUNIFY

At YOUNIFY Clinic, starting targeted therapy or immunotherapy does not begin with the drug. It begins with confirming that an indication supports it and that continuous follow-up is realistic for the patient.

• Consultation and record review — pathology, imaging, biomarker results, treatment history, comorbidities and the current medication list.
• Confirm the indication — check that the biomarker findings match the option under consideration and that there is no significant contraindication.
• Bring the case to the multidisciplinary meeting — so the decision is made collectively rather than read off a report alone. See what a molecular tumour board is.
• Explain before treatment starts — the goal, the side effects to watch for, which symptoms to report immediately, the follow-up schedule, and what remains uncertain.
• Start treatment with structured follow-up — blood tests, symptom review and imaging at appropriate intervals, with a contact route for symptoms between visits.
• Reassess when things change — if the disease progresses, repeat testing from tissue or blood may be considered to look at resistance mechanisms, and the plan revisited.

Where a plan requires chemotherapy, radiotherapy or cancer surgery, the medical team arranges a coordinated referral to a partner facility and helps keep the record continuous between institutions.

If you have been advised to consider one of these treatments and want to understand the mechanism, the monitoring and what to watch for, you can read how the pathway works on our precision oncology service page, or message the team on WhatsApp to ask which documents are worth bringing. Nothing here asks you to move your care — the aim is that you continue with your treating physician, better equipped to ask them what you need to know.