What Tests Are Required Before Molecular Targeted Therapy? (2026 Update)

Molecular targeted therapies only work in patients whose tumors show specific genetic or protein changes, so biomarker testing on tissue or blood is always done before a treatment is selected. No targeted therapy is chosen without test results.

Key Points

• Biomarker testing looks for genetic and protein changes in cancer cells to guide treatment decisions. For solid tumors, tissue obtained through surgery or biopsy is used; for blood cancers or liquid biopsy, a blood draw is used (U.S. National Cancer Institute, NCI).
• Targeted therapies only work in patients who have the relevant target, so treatment is decided only after checking EGFR, ALK, and ROS1 in non-small cell lung cancer; HER2 and CLDN18.2 in gastric cancer; HER2 and hormone receptors in breast cancer; and RAS and BRAF in colorectal cancer (National Cancer Information Center, Korea).
• Biomarker testing is not needed for every patient. It is commonly recommended for metastatic or recurrent cancers and is performed routinely for certain cancers such as non-small cell lung cancer, breast cancer, and colorectal cancer (NCI).
• When tissue is hard to obtain, a blood-based method that analyzes tumor DNA may be used instead. Depending on the test, results can take anywhere from a few days to 2-3 weeks.
• If genetic testing done abroad is recent and covers sufficient markers, it can be used as is. If it is insufficient, tissue slides can be sent for retesting in Korea, or the test can be repeated after the patient arrives in Korea.

Is Genetic Testing the Same as Biomarker Testing?

• No, they are different. Genetic testing looks for inherited mutations, whereas biomarker testing identifies genetic and protein changes within the cancer cells themselves to guide treatment choice (NCI).
• Cancer develops when the growth signals of normal cells malfunction, and the location of that malfunction differs from tumor to tumor. In some lung cancers, the EGFR receptor is continuously switched on; in some gastric cancers, the HER2 protein is present in excessive amounts. Because targeted therapies block only that one specific malfunction, the same drug has little to no effect on patients who lack that particular abnormality.
• This is a major reason why, even with the same type of cancer, one patient may improve on a drug while another sees no change — the difference largely comes down to biomarkers.

What Is the Testing Sequence?

• Step 1 — Immunohistochemistry and genetic testing are performed on tissue slides or paraffin blocks.
• Step 2 — If needed, next-generation sequencing (NGS) is used to check multiple mutations at once.
• Step 3 — If tissue is difficult to obtain, a liquid biopsy approach analyzing tumor DNA from blood may be considered.
• Step 4 — Based on the results (available in a few days to 2-3 weeks), doctors confirm whether the relevant target is present. If present, a matching targeted therapy is considered; if not, other options such as cytotoxic chemotherapy, immunotherapy, surgery, or radiation therapy are reviewed.
• Step 5 — If a drug stops working during treatment, retesting is typically done to identify what change has occurred before moving on to the next drug.

FAQ — What Else Should Be Prepared Before Treatment?

Cancer stage is determined by combining imaging, biopsy, and blood test results. The widely used TNM system evaluates tumor size and extent (T), spread to nearby lymph nodes (N), and spread to distant sites (M) (NCI). This, together with biomarker testing, forms the basic information used to set the treatment plan. When planning chemotherapy, the cancer type, stage of progression, prior treatment history, and coexisting conditions such as diabetes or heart disease are also taken into account (NCI).

FAQ — Can Test Results From Abroad Be Used?

If the results are recent and cover sufficient markers, they can be used as is. If results are missing, outdated, or lack necessary markers, tissue slides can be sent for testing or the test can be repeated after arrival. Patients must inform their medical team of all medications currently being taken — including blood thinners and diabetes medications — as well as any supplements or herbal remedies, along with their ingredient names (NCI). The remote review (pre-arrival review) fee is KRW 1,000,000 (about US$730); if treatment is contracted after the remote review, this amount is deducted from the medical bill.

Sources and Notes

• This article was written based on What to Check Before Treatment, Notes on Targeted Therapy (National Cancer Information Center, Korea; NCCN patient guidelines; U.S. National Cancer Institute, NCI).
• This content is intended to provide general medical information, and actual diagnosis, treatment methods, and outcomes may vary depending on individual conditions. For an accurate diagnosis and treatment plan, please be sure to consult with a medical professional.