If someone has told you that your cancer needs to be tested before your treatment can be decided, and you are sitting at home wondering why the drugs cannot simply start now, I want to reassure you. That testing is not a delay in your care. It is the care. In this article I will explain, slowly and in plain words, what targeted therapy is, why the tumour must be examined at the molecular level first, how these drugs feel to live with, and why they sometimes stop working. My aim is that you finish reading a little calmer and a lot better equipped for the conversation with your own team.
What targeted therapy actually is
For most of the twentieth century, cancer treatment meant surgery, radiotherapy, and chemotherapy. Chemotherapy works by poisoning cells that divide quickly. Cancer cells divide quickly, so they are hit hard — but so are healthy fast-dividing cells in your hair follicles, your gut lining, and your bone marrow. That is why classic chemo often causes hair loss, mouth soreness, and low blood counts. It is a broad weapon, and a genuinely effective one, but it does not distinguish very carefully between friend and foe.
Targeted therapy is a different idea. Instead of attacking all dividing cells, these drugs are designed to block one specific molecule that a particular cancer depends on to grow. Think of it less like a blanket poison and more like jamming one specific part of an engine. If that part is what drives the cancer, jamming it can halt or shrink the tumour while leaving much of the rest of the body relatively undisturbed.
The molecule being blocked is usually a protein — a tiny biological machine on the surface of, or inside, the cancer cell. Many of these proteins are signalling switches. In a healthy cell they turn the instruction to “grow and divide” on and off in a carefully controlled way. In cancer, a fault in the gene that makes the protein can leave the switch jammed in the “on” position, so the cell multiplies without a brake. Targeted drugs are built to fit that specific broken switch and shut it down, or to flag the cell carrying it for destruction.
The core idea is simple: find the exact fault that is driving this cancer, then use a drug shaped to block that fault. No fault, no target — which is exactly why the testing has to come first.
Precision medicine: why the test comes before the drug
You may hear the phrase precision medicine (sometimes “personalised medicine”). It simply means choosing treatment based on the specific biological features of your tumour, rather than on where in the body the cancer started alone. Two people can both have lung cancer that looks identical under an ordinary microscope, yet be driven by completely different molecular faults — and therefore need completely different drugs. Precision medicine is the effort to treat the cancer you actually have, at the molecular level, rather than the average version of it.
This is why biomarker testing (also called molecular testing, genomic testing, or tumour profiling) is essential. A biomarker is a measurable feature of the tumour — usually a specific gene change or protein — that predicts whether a particular targeted drug is likely to help. Giving a targeted drug without first confirming its target is present is like buying a key for a lock you have never seen. If the lock is not there, the key does nothing, and you would take on side effects for no benefit. Testing first is not caution for its own sake; it is what makes the whole approach work.
How the testing is done
- On a tissue sample. Most testing uses the biopsy or surgical sample already taken to diagnose your cancer. Often no new procedure is needed — the laboratory simply runs further analysis on tissue it already holds.
- On a blood sample. Some tumours shed fragments of their DNA into the bloodstream. A “liquid biopsy” can detect certain biomarkers from a simple blood draw, which is useful when tissue is hard to reach, when a biopsy would be risky, or when the tissue sample is too small.
- Single tests versus panels. Sometimes the laboratory looks for one specific marker. Increasingly, laboratories run next-generation sequencing (NGS) — a single test that reads many genes at once, so several possible targets are checked together from one sample. This is efficient and reduces the chance of missing a treatable fault.
Results usually take one to three weeks, sometimes longer for large panels or when a repeat biopsy is required. That wait can feel agonising when every instinct is to start fighting immediately, but it is normal and it is worth it. In most situations a short, deliberate pause to gather good information does not harm your prospects, and a well-matched treatment chosen on solid evidence beats a fast treatment chosen on guesswork. If the waiting is weighing on you, it is entirely fair to ask your team roughly when to expect results and whether anything needs to happen in the meantime.
The common targets — and what they mean
You may see a cluster of letters on your pathology report. These are the names of genes or proteins. Here are the ones you are most likely to encounter, in plain terms. Please hold one principle in mind throughout: the presence of a marker in one cancer does not mean it matters in another. The same gene can be a treatment target in one tumour type and completely irrelevant in a different one. Context is everything, and interpreting that context is your oncologist’s job.
- HER2 — a growth-signal protein that some breast and stomach cancers, and occasionally others, produce in excess. HER2-targeted drugs have been among the most established successes in this whole field, and newer ones can now help some cancers with only low levels of HER2, not just high ones.
- EGFR — the epidermal growth factor receptor, another growth switch. Certain EGFR mutations are important drivers in some non-small-cell lung cancers, and specific pills are designed to block them.
- ALK — a gene that, in some lung cancers, becomes fused to another gene, creating an abnormal, always-on growth signal. ALK inhibitors are built to switch off that fusion, and they can work remarkably well.
- BRAF — a switch in the growth pathway. A particular BRAF change (often written BRAF V600) drives some melanomas and other cancers, and can be blocked, frequently alongside a second drug that closes a common escape route.
- KRAS, including KRAS-G12C — for decades KRAS was considered “undruggable.” Drugs that block the specific KRAS-G12C form now exist for some cancers, a genuine and hard-won recent advance.
- Hormone receptors — many breast and prostate cancers are driven by hormones such as oestrogen or testosterone. Hormone (endocrine) therapies are a long-standing, well-understood, and highly effective way of targeting the cancer’s fuel supply. If you are on one of these, you are already receiving a form of precision treatment, even if no one used that phrase.
- BRCA and other DNA-repair faults — some breast, ovarian, prostate, and pancreatic cancers carry faults in genes such as BRCA1 or BRCA2 that leave the cell poor at repairing its own DNA. A class of drugs called PARP inhibitors exploits that weakness. These faults can be inherited or can arise in the tumour alone, which is one reason genetic counselling is sometimes offered alongside testing.
There is also a newer idea worth knowing about: a small number of markers are tumour-agnostic, meaning the matching drug can be considered regardless of where the cancer started. Examples include certain gene fusions (such as NTRK fusions) and a feature called high microsatellite instability. These are uncommon, but they are precisely the kind of thing a broad sequencing panel is designed to catch — another reason wide testing can be valuable.
There are many more targets than I can list, and the list of actionable ones grows every year. What matters is not memorising the letters, but understanding the logic: your report names the specific fault, and your oncologist matches the drug to it.
The broad classes of these drugs
- Small-molecule inhibitors. Usually taken as a pill. They are small enough to slip inside the cell and block the faulty switch from within. Many drug names in this class end in “-ib” (as in inhibitor).
- Monoclonal antibodies. Larger, laboratory-made proteins, usually given by infusion into a vein. They attach to a target on the cell surface, either blocking a signal or marking the cell for the immune system. Many names in this class end in “-mab” (from monoclonal antibody).
- Antibody-drug conjugates. A clever hybrid: an antibody that homes in on the cancer while carrying a toxic payload, delivering that chemotherapy-like agent directly to the tumour and sparing more of the healthy body. These have become an important and expanding part of treatment for several cancers.
A quick word on where immunotherapy fits, because it is easy to muddle the two. People sometimes group immunotherapy with targeted therapy because both are “modern” drugs, but they work in fundamentally different ways. Immunotherapy takes the brakes off your own immune system so it can recognise and attack the cancer. Targeted therapy blocks a specific molecular driver within the tumour itself. Some treatment plans use both, sometimes together and sometimes in sequence. If you are ever unsure which one you are actually on, that is a good, simple question for your team — and knowing the answer helps you understand your side effects, too.
Who is targeted therapy for?
Targeted therapy is an option only when your tumour carries a fault that a matching drug can block. This is the honest heart of the matter. These drugs can be remarkable, but they are not universal, and it would do you no kindness to imply otherwise. Broadly, whether targeted therapy is on the table depends on three things:
- Your cancer type. Some cancers — certain lung cancers, breast cancers, melanomas, and several blood cancers among them — have well-established targets and approved drugs. Others currently have few or none, though research is active across the board.
- Your specific biomarker results. Even within one cancer type, only some tumours carry a targetable fault. If your test is negative for a driver, it does not mean your care is second-rate — it means a different approach is the better fit for you.
- The stage and goal of treatment. Some targeted drugs are used for advanced disease to control it; others are given after surgery to lower the chance of the cancer returning. The same drug can play very different roles depending on the situation.
If your report comes back without an actionable target, please do not read that as bad luck about the quality of your care. Chemotherapy, immunotherapy, radiotherapy, hormone therapy, and surgery remain powerful, and for many cancers they are the mainstay for very good reasons. Precision medicine is one excellent tool in a well-stocked toolbox — not the only good one, and not always the right one.
How targeted therapy fits with your other treatments
It is a common misunderstanding that a targeted drug replaces everything else. Sometimes it does stand alone, but very often it works as one part of a larger plan. Depending on your cancer, a targeted therapy might be combined with chemotherapy, paired with a second targeted drug to close off an escape route, added to hormone therapy, or given after surgery or radiotherapy to mop up any cells left behind. In some cases it is used first to shrink a tumour before an operation. None of this is contradictory — it reflects the fact that cancer is complicated and the best results often come from thoughtful combinations rather than a single silver bullet. If the plan your team proposes has several moving parts, that is usually a sign of care, not confusion, and it is always fair to ask them to walk you through how the pieces fit together and in what order.
What to expect day to day
One of the quiet advantages of many targeted therapies is that they are taken as a pill at home, often once or twice a day, rather than requiring long infusion sessions in a chemotherapy suite. This can mean fewer hospital visits and more ordinary life. But “a pill at home” carries its own responsibilities, and taking them seriously is part of making the treatment work:
- Take it exactly as prescribed. Consistent timing keeps the level of the drug in your blood steady, which is what keeps the target reliably blocked. Ask whether to take it with or without food — it genuinely changes how well some of these medicines are absorbed.
- Ask about interactions. Some targeted pills interact with common medicines, supplements, and even grapefruit and its juice. Give your pharmacist a complete list of everything you take, including over-the-counter remedies and herbal products, and check before adding anything new.
- Do not stop or change the dose on your own. If side effects are troubling you, contact your team rather than quietly reducing or skipping doses. There is very often a solution — a lower dose, a short planned break, or a supportive medicine — that keeps you on treatment safely and comfortably.
- Keep your monitoring appointments. You will usually have regular scans and blood tests, both to confirm the drug is working and to check it is not quietly straining your heart, liver, thyroid, or other organs. These appointments are not a formality; they are how problems are caught early.
- Store the medicine safely. Some of these drugs need particular storage, and all should be kept well away from children and others. Your pharmacist will tell you how to handle and, if ever needed, dispose of them.
How the side effects differ from chemotherapy
Because targeted drugs do not broadly poison every fast-dividing cell, they often spare people the classic chemo experience — the dramatic hair loss and the steep drop in blood counts are frequently less prominent. But “different” does not mean “none,” and I would not want you to be caught off guard. These drugs have their own characteristic side effects, and a few can be serious. Exactly which ones you might face depends entirely on your specific drug, and your team will tell you what to watch for with yours.
Common patterns include:
- Skin changes. A rash, dryness, or acne-like spots are especially common with drugs that block EGFR and related pathways, because those same pathways help keep skin healthy. Interestingly, with some of these drugs a rash can even be a sign that the medicine is engaging its target, though it still deserves attention and treatment.
- Digestive effects. Diarrhoea is frequent with several targeted drugs. Report it early, because it can usually be managed well, and if left unchecked it can lead to dehydration.
- Blood pressure changes. Some drugs, particularly those that interfere with the growth of blood vessels, can raise blood pressure, which is why it is monitored during treatment.
- Fatigue, and changes to nails, hair texture, or the mouth. Often milder, but real, and worth mentioning at appointments so they can be eased.
- Organ-specific effects. Depending on the drug, effects on the liver, heart, thyroid, or lungs are possible. This is precisely why regular blood tests and scans are built into the plan — to spot and manage such things before they become serious.
None of this is meant to frighten you. Most side effects are manageable, and the goal of all that monitoring is to keep you well enough to stay on a treatment that is helping. The single most useful thing you can do is report new symptoms early rather than waiting to see whether they pass.
When to contact your team — and when it is urgent
Please keep the contact number your team gave you somewhere you can find it quickly, including late at night. As a general guide — and always following the specific instructions your own team gave you, which take priority over anything here — contact them promptly for:
- Diarrhoea that is frequent, does not settle, or comes with dizziness or a noticeable drop in how much you are passing water.
- A rash that is spreading, blistering, weeping, or painful.
- A new fever, especially if you also feel generally unwell — on cancer treatment this is never something to sit on.
- Any side effect that is getting steadily worse rather than settling.
Seek emergency care straight away for chest pain, sudden breathlessness, coughing up blood, severe or rapidly worsening pain, signs of a severe allergic reaction (swelling of the face, lips, or throat, or difficulty breathing), or any symptom that genuinely frightens you. It is always right to ask, and it is always better to be checked and reassured than to wait. Teams would far rather hear from you early than late — that is what they are there for.
Why resistance develops
Here is the part I most want to be honest with you about, because unexpected news is so much harder to bear than news you saw coming. Even when a targeted therapy works beautifully at first, it often stops working over time. This is called resistance, and I want to say clearly: it is not a failure on your part, and it is not a sign you did anything wrong.
The reason lies in the nature of cancer itself. A tumour is not one uniform thing; it is a shifting, restless population of cells that keep mutating. When a drug blocks one specific driver, it clears away the cells that depend on that driver — but a few cells may already carry, or later develop, a different fault that lets them grow around the blockade. Over months, or sometimes years, those cells can multiply, and the drug that once held the cancer in check no longer does. The tumour has, in effect, evolved. This is biology doing what biology does, not a verdict on you.
What this means in practice:
- Resistance is expected, not shocking. Your team plans for it from the start. A drug that works well for a good stretch of time is a real success, even when it does not work forever.
- There are often next steps. When resistance appears, repeat biomarker testing — sometimes through a liquid biopsy — can reveal the new fault behind it. In some cancers a next-generation drug has been designed precisely to overcome a known resistance change, so the specific reason a drug stopped working can point directly to what comes next.
- The field keeps moving. New targeted drugs and combinations continue to be approved, and clinical trials are a legitimate, sometimes excellent option worth asking about — not a last resort, but a route to tomorrow’s treatment today.
A word on access, cost, and second opinions
Because I write for readers all over the world, I want to be plain about something the science alone does not cover: access to biomarker testing and to these drugs varies a great deal between countries and health systems. In some places comprehensive testing is routine; in others it must be specifically requested, or is available mainly through larger cancer centres or clinical trials. If targeted therapy has not been mentioned and you have reason to think it might apply to your cancer, it is entirely reasonable — and not at all rude — to ask your oncologist whether biomarker testing is appropriate for you and whether it has been done. Asking for a second opinion, or a referral to a specialist centre, is a normal and accepted part of cancer care, not a slight against your current team. Good clinicians expect these questions and welcome them.
Common myths, gently corrected
- “Targeted therapy is a cure.” For some cancers it produces long, durable control, and for a few it is part of a curative plan; for many advanced cancers it controls the disease for a meaningful period rather than curing it. Both outcomes matter. Ask your team what the realistic goal is in your particular case.
- “Because it’s targeted, it has no side effects.” Not so — the side effects are simply different from those of chemotherapy, and some need close monitoring.
- “A pill is weaker than an infusion.” The route of delivery says nothing about how powerful a drug is. Many oral targeted therapies are highly effective; the pill form is a convenience, not a compromise.
- “If I have this cancer, I must have the marker.” Only some tumours of a given type carry a targetable fault. That is exactly why the test is done rather than assumed.
- “Testing is only for the wealthy or for research.” Biomarker testing is now standard practice for several cancers. Where it is not automatic, it is still reasonable to ask whether it applies to you.
What to write down and ask your team
When you are anxious, questions have a way of evaporating the moment you sit down in the room. Take a list on your phone, and do not worry about asking too much:
- Has my tumour been tested for biomarkers, and can you explain my results in plain words?
- Is a targeted therapy an option for me, and what is its goal — to cure, to control, or to lower the chance of the cancer returning?
- Which specific side effects should I watch for with this drug, and which of them need urgent contact?
- Is it a pill or an infusion? Should I take it with or without food? Are there interactions with my other medicines or supplements?
- How will we know if it is working, and what happens if it stops working?
- Are there clinical trials I should consider, now or later?
- Would a second opinion or referral to a specialist centre be worthwhile in my situation?
What to take from this
- Targeted therapy blocks a specific molecule driving your cancer, rather than broadly poisoning all dividing cells the way classic chemotherapy does.
- Biomarker testing comes first and is essential — the drug is chosen to match a confirmed fault such as HER2, EGFR, ALK, BRAF, KRAS-G12C, a hormone receptor, or a DNA-repair fault like BRCA.
- Many of these drugs are pills taken at home, which means fewer infusions but a real responsibility for timing, interactions, and keeping monitoring appointments.
- Side effects differ from chemo — think rash, diarrhoea, and blood-pressure changes rather than hair loss — and a few need prompt or emergency attention.
- Resistance often develops over time as the tumour evolves, which is expected and frequently opens the door to a next line of treatment or a clinical trial.
- Access varies, and questions are welcome — asking about testing, goals, and second opinions is a normal part of good cancer care.
Everything here is general education, not a treatment decision for your particular situation. Your own oncology team knows your test results, your cancer, and your body in a way no article ever can. Take these questions to them, and let them help you match the right approach to you.