Targeted Therapy for Cancer: How It Works and Who Benefits

Targeted therapy is a class of cancer treatment that blocks specific molecular alterations — mutations, gene amplifications, chromosomal rearrangements — that cancer cells depend on to grow and survive. Unlike chemotherapy, which kills any rapidly dividing cell, targeted therapy drugs act selectively on cancer cells carrying a specific molecular target, leaving most normal cells relatively unaffected.

The fundamental requirement for targeted therapy is a biomarker: the molecular alteration must be confirmed in the patient’s tumor before prescribing. The same cancer type in two different patients may have entirely different driver mutations — and different targeted therapy options, or none at all. This is the core of precision oncology: treatment matched not to the organ where cancer originated, but to the molecular alteration driving its growth. For how targeted therapy compares to all treatment modalities, see the cancer treatment options guide. For a mechanistic comparison with chemotherapy, see the chemotherapy guide.

38.6 vs. 31.8 mo Overall survival: osimertinib vs. first-gen EGFR TKI for EGFR-mutant NSCLC (FLAURA trial)

28.8 vs. 6.8 mo Progression-free survival: T-DXd vs. T-DM1 for HER2+ metastatic breast cancer (DESTINY-Breast03)

>80% 10-year overall survival for CML patients on imatinib (IRIS trial) — vs. median survival <5 years before TKIs

75% Overall response rate for NTRK fusion-positive cancers with larotrectinib — regardless of tumor type (tissue-agnostic FDA approval)

How Targeted Therapy Works

Cancer cells accumulate genetic alterations — point mutations, amplifications, deletions, fusions — that activate signaling pathways driving uncontrolled proliferation, survival, and invasion. Targeted therapy drugs block the specific altered protein — the driver — interfering with the signal the cancer cell uses to divide and survive. Normal cells, which typically don’t carry the alteration, are relatively unaffected.

Small Molecule Inhibitors (SMIs)

Oral drugs small enough to cross cell membranes. Most are tyrosine kinase inhibitors (TKIs) blocking intracellular kinase domains. Include EGFR TKIs, ALK TKIs, BRAF inhibitors, CDK4/6 inhibitors, BTK inhibitors, PARP inhibitors, KRAS G12C inhibitors.

Monoclonal Antibodies (mAbs)

Large proteins given by IV infusion. Bind extracellular targets — HER2 receptor, VEGF ligand, EGFR. Blocking receptor activation, triggering immune destruction (ADCC), or cutting off tumor blood supply.

Antibody-Drug Conjugates (ADCs)

Guided missile: monoclonal antibody + cytotoxic payload via cleavable chemical linker. Delivers high-concentration chemotherapy specifically to target-expressing cancer cells. T-DXd, sacituzumab govitecan, enfortumab vedotin are the key approved ADCs.

Targeted Therapy Drug Classes in Detail

EGFR and ALK Inhibitors (Lung Cancer)

Osimertinib (third-generation EGFR TKI) is the first-line standard for EGFR-mutant NSCLC (exon 19 deletion or L858R point mutation) — the most common targetable alteration in lung cancer (~15% of Western, ~50% of Asian patients with NSCLC):

FLAURA trial (NEJM 2018): osimertinib vs. first-generation EGFR TKI: OS 38.6 vs. 31.8 months; PFS 18.9 vs. 10.2 months; superior CNS activity
ADAURA trial (NEJM 2020): adjuvant osimertinib for 3 years after resection of EGFR-mutant NSCLC Stage IB–IIIA: 2-year DFS 90% vs. 44% (HR 0.17) — one of the largest DFS benefit effects in an adjuvant oncology trial

ALK TKIs target the EML4-ALK rearrangement (~5% of NSCLC):

Alectinib (ALEX trial, NEJM 2017): PFS 34.8 vs. 10.9 months vs. crizotinib; superior CNS efficacy — critical because ~30% of ALK+ patients develop brain metastases
Lorlatinib (CROWN trial): 3-year PFS 63.5% vs. 19% vs. crizotinib; deepest CNS penetration of any ALK TKI; now preferred first-line

BCR-ABL Inhibitors (CML) — A Transformative Success Story

The Philadelphia chromosome creates the BCR-ABL1 fusion tyrosine kinase — the sole oncogenic driver of CML. Imatinib (Gleevec), approved in 2001, transformed CML from a disease with median survival under 5 years to one with >80% 10-year overall survival (IRIS trial) — the most dramatic single targeted therapy success in oncology. Second-generation inhibitors (dasatinib, nilotinib) and the novel STAMP inhibitor asciminib address resistance. Approximately 40–50% of patients who achieve deep molecular remission can successfully stop TKI therapy and maintain treatment-free remission.

BRAF + MEK Inhibitors (Melanoma and Other Cancers)

BRAF V600E/K mutations (~50% of melanomas, ~2% of NSCLC, ~8–10% of CRC). BRAF inhibitors alone cause paradoxical ERK activation through feedback — combination with MEK inhibitors prevents this and delays resistance. Dabrafenib + trametinib (COMBI-d/v trials): 5-year OS 34% in metastatic melanoma — a cancer that was uniformly fatal within months before targeted therapy. BRAF V600E is also targetable in CRC: BEACON-CRC trial (encorafenib + cetuximab): OS 9.3 vs. 5.4 months vs. control.

CDK4/6 Inhibitors (HR+/HER2- Breast Cancer)

Palbociclib, ribociclib, and abemaciclib block cyclin D-CDK4/6 kinase complexes that drive the G1/S cell cycle transition. Combined with aromatase inhibitors or fulvestrant in metastatic HR+/HER2- breast cancer:

PALOMA-2: Palbociclib + letrozole: PFS 24.8 vs. 14.5 months vs. letrozole alone
MONARCH 2: Abemaciclib + fulvestrant: OS 46.7 vs. 37.3 months
MONALEESA-7: Ribociclib in premenopausal patients: 5-year OS 70.2% vs. 46.0%

KRAS G12C Inhibitors — The Undruggable Target Made Druggable

40 Years of “Undruggable” — Then Sotorasib Changed Everything

KRAS has been one of the most frequently mutated oncogenes in human cancer since identified in 1982 — and was considered undruggable for four decades because its smooth protein surface offered no obvious drug-binding site. The discovery of a previously unrecognized pocket adjacent to the KRAS G12C switch II region enabled covalent inhibitor design. Sotorasib (AMG 510) achieved ORR 37.1% in pre-treated KRAS G12C-mutant NSCLC (CodeBreaK 100, NEJM 2021) — the first KRAS inhibitor approved in oncology.

KRAS G12C inhibitors: sotorasib (ORR 37.1%) and adagrasib (KRYSTAL-1: ORR 42.9%) are approved for KRAS G12C NSCLC second-line after platinum + checkpoint inhibitor. Active investigation ongoing for KRAS G12C CRC and pancreatic cancer.

PARP Inhibitors — Synthetic Lethality in BRCA-Mutated Cancers

PARP inhibitors exploit synthetic lethality: cancer cells with BRCA1 or BRCA2 mutations cannot repair DNA double-strand breaks via homologous recombination. They rely on PARP-mediated single-strand break repair. When PARP inhibitors block and trap PARP on DNA, accumulated double-strand breaks become lethal — but only in BRCA-deficient cells. Normal cells with intact BRCA survive.

Olaparib (Lynparza) across cancer types:

SOLO1 (BRCA1/2-mutated advanced ovarian): maintenance PFS 60.4 vs. 13.8 months — one of the largest PFS effects in gynecologic oncology
OlympiA (BRCA1/2-mutated early breast cancer): adjuvant: improved invasive DFS at 3 and 4 years
POLO (BRCA1/2-mutated metastatic pancreatic): maintenance PFS 7.4 vs. 3.8 months
PROfound (BRCA1/2-mutated mCRPC): OS 19.1 vs. 14.7 months

Monoclonal Antibodies and ADCs

Trastuzumab + pertuzumab dual HER2 blockade (CLEOPATRA trial): OS 57.1 vs. 40.8 months — the most durable OS benefit reported in first-line HER2+ metastatic breast cancer; now the standard regimen for HER2+ metastatic breast cancer first-line.

Trastuzumab deruxtecan (T-DXd / Enhertu) — the most impactful ADC of the current era. The HER2-targeting antibody is linked to DXd (topoisomerase I inhibitor) via a highly cleavable linker. DXd release within tumor lysosomes kills the targeted cell AND diffuses into adjacent cells (bystander effect), relevant for tumors with heterogeneous HER2 expression:

DESTINY-Breast03: HER2+ MBC second-line: PFS 28.8 vs. 6.8 months vs. T-DM1; OS also superior → new second-line standard
DESTINY-Breast04: HER2-low MBC (IHC 1+ or 2+/ISH-): OS 23.4 vs. 16.8 months — first evidence that “HER2-low” is a clinically actionable target, potentially expanding HER2-targeting to ~50–60% of all metastatic breast cancer patients
Also approved: HER2-mutant NSCLC (DESTINY-Lung02: ORR 57.7%), HER2+ gastric cancer

Enfortumab vedotin + pembrolizumab (EV-302/KEYNOTE-A39): urothelial carcinoma first-line: PFS 12.5 vs. 6.3 months vs. platinum-based chemotherapy; OS superiority confirmed — replaced platinum-based chemotherapy as the first-line standard for metastatic urothelial carcinoma.

Biomarker Testing — The Prerequisite for Targeted Therapy

A targeted therapy without its target is either ineffective or potentially harmful. Before prescribing, the tumor must be tested for the specific molecular alteration the drug requires.

Test Type	What It Detects	When Used
IHC (Immunohistochemistry)	Protein overexpression: HER2 (3+ = amplified; 2+ equivocal → ISH); ER/PR; PD-L1	Breast cancer, gastric, lung
PCR	Specific mutations: EGFR ex19del/L858R/T790M; BRAF V600E; KRAS; IDH1/2	Fast single-gene confirmation
NGS / CGP	All SNVs, fusions, CNVs, TMB, MSI-H — simultaneously	Metastatic NSCLC, CRC, bladder, melanoma — recommended upfront (NCCN)
Liquid biopsy (ctDNA)	Cell-free tumor DNA from blood: EGFR T790M resistance; emerging resistance mutations	When tissue unavailable; resistance monitoring
Companion diagnostics	FDA-required specific test for specific drug	EGFR cobas test (erlotinib/osimertinib); Vysis ALK FISH (crizotinib/alectinib)

Comprehensive Genomic Profiling (CGP) using FDA-approved platforms (FoundationOne CDx, Caris, Tempus) can simultaneously identify all actionable molecular alterations from a single tissue biopsy — and reveal clinical trial eligibility for rare alterations. NCCN recommends upfront broad molecular profiling for all newly diagnosed metastatic NSCLC, colorectal, bladder, and other biomarker-rich cancers. Asking your oncologist what testing was done on your tumor — and whether CGP was performed — is one of the most important questions before starting treatment. See the cancer diagnosis questions guide.

targeted therapy cancer biomarker molecular testing precision oncology — Precision oncology: tumor biomarker testing identifies the molecular alteration that determines which targeted therapy to use — the same cancer type in two patients may require entirely different treatments.

Targeted Therapy by Cancer Type

Cancer Type	Molecular Target	Drug / Key Trial	Key Result
NSCLC	EGFR ex19del/L858R	Osimertinib (FLAURA)	OS 38.6 vs. 31.8 mo
NSCLC	ALK rearrangement	Lorlatinib (CROWN); Alectinib (ALEX)	3-yr PFS 63.5% (lorlatinib)
NSCLC	KRAS G12C	Sotorasib (CodeBreaK 100)	ORR 37.1% 2L
HER2+ Breast	HER2 amplification	T-DXd (DESTINY-Breast03)	PFS 28.8 vs. 6.8 mo 2L
HER2-low Breast	HER2 IHC 1+ or 2+/ISH-	T-DXd (DESTINY-Breast04)	OS 23.4 vs. 16.8 mo
HR+/HER2- Breast	CDK4/6 pathway	Palbociclib/Ribociclib/Abemaciclib	PFS 24.8 mo (PALOMA-2)
HR+/HER2- Breast	PIK3CA mutation	Alpelisib + fulvestrant (SOLAR-1)	PFS 11.0 vs. 5.7 mo
Melanoma	BRAF V600E	Dabrafenib + trametinib (COMBI-d/v)	5-yr OS 34%
CRC	BRAF V600E	Encorafenib + cetuximab (BEACON-CRC)	OS 9.3 vs. 5.4 mo
CML	BCR-ABL fusion	Imatinib → dasatinib → asciminib (IRIS)	10-yr OS >80%
Urothelial	Nectin-4 (ADC)	Enfortumab vedotin + pembro (EV-302)	PFS 12.5 vs. 6.3 mo 1L
Any NTRK fusion	NTRK gene fusion	Larotrectinib (tissue-agnostic)	ORR 75%
BRCA-mutated cancers	BRCA1/2 mutation	Olaparib (SOLO1, OlympiA, POLO, PROfound)	60.4 vs. 13.8 mo PFS (ovarian)

Tissue-Agnostic Approvals

Some targeted therapies are approved based on a molecular alteration — regardless of which organ the cancer originated from:

NTRK fusion Larotrectinib or entrectinib: ORR ~75% in any solid tumor
MSI-H/dMMR Pembrolizumab or dostarlimab: approved for any solid tumor with microsatellite instability-high
TMB-H ≥10 Pembrolizumab: tumor mutational burden-high in any solid tumor (KEYNOTE-158)
RET fusion Selpercatinib or pralsetinib: any solid tumor with RET gene fusion

Tissue-agnostic approvals represent a conceptual shift: the biomarker — not the organ — determines which drug is used.

Resistance to Targeted Therapy

Nearly all patients with metastatic disease treated with targeted therapy eventually develop resistance. Resistance mechanisms include:

On-target resistance: A secondary mutation in the same gene being targeted. After first-generation EGFR TKIs, ~60% develop EGFR T790M gatekeeper mutation → osimertinib overcomes it. After osimertinib, C797S can emerge. In CML, T315I is resistant to all first- and second-generation TKIs → ponatinib or asciminib.
Bypass tract resistance: A downstream pathway activates without passing through the inhibited target. MET amplification after EGFR TKI bypasses EGFR signaling entirely. RET fusions can emerge after osimertinib.
Histologic transformation: EGFR-mutant NSCLC can transform to small cell lung cancer (~5% after osimertinib) — then requires SCLC chemotherapy regimens, not continued EGFR TKI.

The clinical response to resistance is re-biopsy (tissue or liquid biopsy) to identify the mechanism, then selection of a drug that addresses it. The cycle of response → resistance → re-biopsy → new targeted therapy → response is now the standard management paradigm for oncogene-driven cancers. For information on how hormone therapy works as a form of endocrine-targeted treatment for breast and prostate cancers, see the upcoming hormone therapy cancer guide. For the overview of all cancer treatment approaches, see the cancer treatment guide.

Frequently Asked Questions

What is targeted therapy for cancer?

Targeted therapy is a type of cancer treatment that blocks specific molecular alterations — mutations, gene amplifications, chromosomal fusions — that cancer cells carry and depend on for growth. Unlike chemotherapy, which kills any rapidly dividing cell, targeted therapy selectively attacks cancer cells carrying the specific target while sparing most normal cells. Examples include osimertinib for EGFR-mutant lung cancer, trastuzumab for HER2-amplified breast cancer, imatinib for BCR-ABL fusion in CML, and olaparib for BRCA1/2-mutated ovarian cancer. According to the National Cancer Institute, targeted therapy is now standard treatment for many cancer types and has transformed outcomes in diseases previously treated only with chemotherapy.

How is targeted therapy different from chemotherapy?

Chemotherapy kills all rapidly dividing cells — cancer cells and normal rapidly dividing tissues alike (bone marrow, gut epithelium, hair follicles) — causing myelosuppression, nausea, alopecia, and neuropathy. Targeted therapy specifically attacks cancer cells carrying a defined molecular alteration, sparing cells without the target. Side effect profiles are entirely different: EGFR TKIs cause rash and diarrhea; CDK4/6 inhibitors cause fatigue and mild neutropenia; BRAF + MEK inhibitors commonly cause fever; T-DXd can cause interstitial lung disease — none of which are chemotherapy side effects. Many targeted therapies are oral pills taken daily rather than IV infusions. The critical difference: targeted therapy requires biomarker confirmation. Chemotherapy does not. See the chemotherapy guide for a detailed comparison of drug classes and mechanisms.

What biomarker tests are needed before starting targeted therapy?

Required tests depend on cancer type. For metastatic NSCLC, NCCN recommends upfront comprehensive genomic profiling (NGS) to simultaneously test for EGFR, ALK, ROS1, BRAF, KRAS G12C, MET exon 14, RET, NTRK, HER2, and PD-L1. For breast cancer: HER2 IHC and FISH, ER/PR, germline BRCA1/2, and PIK3CA mutation (before alpelisib). For CRC: KRAS/NRAS/BRAF, MSI/MMR, and HER2. NGS/comprehensive genomic profiling (CGP) using platforms like FoundationOne CDx, Caris, or Tempus can detect all relevant alterations from a single tissue biopsy. Liquid biopsy (blood-based ctDNA) is increasingly used for initial testing and resistance monitoring. The FDA’s hematology/oncology approval list shows which companion diagnostic is required for each drug.

What are the side effects of targeted therapy?

Side effects are drug- and mechanism-specific — unlike chemotherapy’s broad toxicities. Common patterns by drug class: EGFR TKIs (osimertinib, erlotinib) → acneiform rash, diarrhea, paronychia (nail inflammation), rare interstitial lung disease; CDK4/6 inhibitors → mild neutropenia (less clinically significant than chemo-related), fatigue, nausea; ALK TKIs (alectinib) → myalgia, mild bradycardia, elevated creatinine; BRAF + MEK inhibitors → pyrexia (fever, very common ~70% with dabrafenib + trametinib), photosensitivity, fatigue; BTK inhibitors (ibrutinib) → atrial fibrillation, bruising, bleeding, hypertension (acalabrutinib has fewer cardiac events); trastuzumab → infusion reactions, cardiac toxicity (monitor LVEF); T-DXd → interstitial lung disease (serious; 2–3% grade 3–4; monitor for breathlessness/cough); PARP inhibitors → nausea, fatigue, anemia. Unlike chemotherapy, most targeted therapies do not cause severe myelosuppression or alopecia.

What is an antibody-drug conjugate (ADC)?

An antibody-drug conjugate (ADC) is a targeted therapy that combines a monoclonal antibody (designed to bind a specific protein on cancer cells) with a cytotoxic payload connected via a chemical linker. The antibody delivers the payload specifically to cancer cells expressing the target protein, where the linker is cleaved and the cytotoxin is released — achieving high drug concentrations inside cancer cells while limiting systemic exposure. The most impactful recent ADC is trastuzumab deruxtecan (T-DXd / Enhertu): HER2-targeting antibody + DXd topoisomerase I inhibitor payload. DESTINY-Breast03 showed PFS 28.8 vs. 6.8 months vs. T-DM1 in HER2+ metastatic breast cancer; DESTINY-Breast04 showed OS 23.4 vs. 16.8 months in HER2-low disease — extending HER2-directed therapy to patients previously considered HER2-negative. T-DXd’s bystander effect (the released DXd diffuses into adjacent cells) explains its activity even in tumors with heterogeneous HER2 expression.

Does targeted therapy work for all cancers?

No — targeted therapy only works when the cancer carries the specific molecular alteration the drug targets. A patient whose tumor has no EGFR mutation will not benefit from an EGFR TKI. KRAS inhibitors (sotorasib, adagrasib) only work for the specific KRAS G12C mutation — not other KRAS mutations. Some cancers have well-characterized, frequently occurring driver alterations — EGFR mutation in NSCLC, BCR-ABL in CML, HER2 amplification in HER2+ breast cancer — making targeted therapy reliably applicable. Other cancers (triple-negative breast cancer, most pancreatic and glioblastoma) have complex mutational landscapes without a consistently druggable single driver, though exceptions exist (BRCA1/2-mutated TNBC; KRAS G12C in some pancreatic cancers). Tissue-agnostic approvals (NTRK fusion: ORR ~75% regardless of tumor type) show that the alteration — not the organ — matters most. Comprehensive genomic profiling at diagnosis can reveal rare targetable alterations that standard single-gene testing would miss.

Soria JC et al. / Wu YL et al. — FLAURA (osimertinib 1L NSCLC); NEJM 2018 / 2019
Wu YL et al. — ADAURA (adjuvant osimertinib); NEJM 2020
Peters S et al. — ALEX (alectinib vs. crizotinib ALK+ NSCLC); NEJM 2017
Solomon BJ et al. — CROWN (lorlatinib vs. crizotinib); NEJM 2020
Long GV et al. — COMBI-d/v (dabrafenib + trametinib melanoma); Lancet 2015; 5-yr update 2017
Swain SM et al. — CLEOPATRA (pertuzumab + tras HER2+ MBC); Lancet Oncology 2013
Cortés J et al. — DESTINY-Breast03 (T-DXd vs. T-DM1); NEJM 2022
Modi S et al. — DESTINY-Breast04 (T-DXd HER2-low); NEJM 2022
Finn RS et al. — PALOMA-2 (palbociclib + letrozole); NEJM 2016
Kopetz S et al. — BEACON-CRC (encorafenib + cetuximab BRAF V600E CRC); NEJM 2019
Skoulidis F et al. — CodeBreaK 100 (sotorasib KRAS G12C NSCLC); NEJM 2021
Moore K et al. — SOLO1 (olaparib ovarian); NEJM 2018
Hochhaus A et al. — IRIS 10-year follow-up (imatinib CML); Leukemia 2017
National Cancer Institute — Targeted Therapy to Treat Cancer
FDA — Hematology/Oncology Cancer Approvals & Safety Notifications

This article is for educational purposes only and does not constitute medical advice. Discuss all targeted therapy decisions with your oncology care team.