Targeted therapy refers to drugs designed to attack specific molecular features of cancer cells, most often abnormal proteins produced by genetic mutations. If chemotherapy is like 'carpet bombing that does not distinguish friend from foe,' targeted drugs are like 'precision-guided missiles that lock onto their target'—they interfere with the specific signals cancer cells depend on to survive, with relatively less impact on normal cells.
Targeted therapy is a hallmark of the precision medicine era: over the past two decades, it has reshaped the treatment landscape for lung cancer, breast cancer, colorectal cancer, leukemia, and many other cancers, turning some advanced cancers into chronic diseases that can be controlled long term.
How It Works
Cancer cell growth depends on certain abnormally active signaling pathways, and these abnormalities are often driven by specific genetic mutations—for example, EGFR mutations and ALK fusions in lung cancer, HER2 amplification in breast cancer, and RAS/BRAF status in colorectal cancer. Targeted drugs act like specially made keys that fit into the 'keyholes' of these abnormal proteins, cutting off the growth instructions to cancer cells.
There are two main categories of targeted drugs: small-molecule inhibitors (mostly oral drugs that enter cells to block enzyme activity, such as EGFR inhibitors) and monoclonal antibodies (injectable drugs that bind targets outside cells, such as anti-HER2 antibodies). In recent years, antibody-drug conjugates (ADCs) have also emerged—combining the precision of antibodies with the killing power of chemotherapy drugs—along with new breakthroughs against previously 'undruggable' targets such as RAS.
When It Is Used
The prerequisite for targeted therapy is having a target to hit: genetic testing (usually next-generation sequencing, NGS) must first confirm that the tumor carries the corresponding mutation. The most classic example is advanced non-small cell lung cancer—for patients with EGFR, ALK, ROS1, or other mutations, oral targeted drugs are the first choice, with better efficacy than chemotherapy and milder side effects.
Other common applications include anti-HER2 therapy for HER2-positive breast and gastric cancers, anti-EGFR drugs for colorectal cancer (only in patients without RAS mutations), PARP inhibitors for cancers with BRCA alterations, anti-angiogenic drugs for kidney and liver cancers, and 'tumor-agnostic' targeted drugs for rare fusion genes (NTRK, RET). Targeted drugs are also increasingly used in adjuvant and neoadjuvant settings after surgery.
Common Side Effects and Management
The side effects of targeted drugs are usually milder than those of chemotherapy, but they are not absent. Common ones include: rash and paronychia (typical reactions to EGFR inhibitors, manageable with ointments and oral medications), diarrhea (stay hydrated; dose adjustment may be needed if severe), and abnormal liver function (monitored with regular blood tests).
Anti-angiogenic drugs may cause high blood pressure, protein in the urine, and wound-healing problems; anti-HER2 drugs require monitoring of heart function. The key principle is 'report early, manage early'—most side effects are controllable after dose adjustment or supportive treatment. Never stop medication on your own.
Drug Resistance: The Essential Question in Targeted Therapy
The common fate of targeted drugs is this: significant benefit at first, then after a period of time the cancer cells find new escape routes and resistance develops. This is not treatment failure but the norm in cancer care—after resistance, repeat testing (tissue or blood genetic testing) often reveals new targets, allowing treatment to continue with next-generation drugs.
Take EGFR lung cancer as an example: after resistance to a first-generation drug, if the T790M mutation appears, patients can switch to a third-generation drug; after resistance to the third-generation drug, combination regimens and ADC drugs can take over. This 'relay-style' treatment is the foundation for turning advanced cancer into a chronic disease.
Clinical Trials: One More Treatment Option
Almost all targeted drugs were born from clinical trials, and patients after resistance are exactly the population best suited for trials—new-target drugs, next-generation inhibitors, and combination strategies are all waiting to be validated.
The CancerLink platform can screen for clinical studies recruiting in Hong Kong based on cancer type, stage, and genetic mutations. After successful matching and enrollment, study-related treatment costs are fully covered. Please keep your genetic testing report safe—it is your passport to trial matching.
If you have been diagnosed with advanced cancer, remember to proactively ask your doctor one question: 'Has my tumor had genetic testing?' A complete testing report may directly change your treatment path—from chemotherapy to one oral targeted pill a day.