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Targeted Cancer Therapy: Biomarkers, TKIs & Molecular Protocols

Q: What is targeted therapy and how is it different from chemotherapy?

Targeted therapy focuses on specific molecular alterations, proteins, or genes that drive cancer growth and survival (such as EGFR, ALK, HER2, or BRAF). Unlike conventional chemotherapy which attacks all rapidly dividing cells, targeted drugs specifically inhibit oncogenic pathways, resulting in higher precision and distinct toxicity profiles.

Q: Why is Next-Generation Sequencing (NGS) required before starting targeted therapy?

Targeted drugs work only if the patient's tumor harbors the matching molecular alteration. Comprehensive Genomic Profiling (CGP) via tissue or liquid biopsy (ctDNA) identifies targetable point mutations, gene amplifications, and fusions, ensuring patients receive the correct matched inhibitor.

Q: What are Tyrosine Kinase Inhibitors (TKIs)?

Tyrosine Kinase Inhibitors are small molecule oral compounds that penetrate cellular membranes to block intracellular kinase enzymatic domains, preventing downstream signaling cascades that instruct tumor cells to proliferate and evade apoptosis.

Q: How do PARP inhibitors work against BRCA-mutated tumors?

PARP inhibitors exploit a concept called 'synthetic lethality.' In cells harboring defective homologous recombination DNA repair (e.g., BRCA1 or BRCA2 mutations), inhibiting PARP prevents base excision single-strand repair, causing catastrophic double-strand breaks that selectively kill cancer cells while sparing normal cells.

Q: How is acquired drug resistance managed in targeted oncology?

Cancers often develop secondary resistance mutations (e.g., EGFR T790M or C797S) or bypass activation pathways (MET amplification). Repeat liquid biopsy or tissue re-biopsy detects resistance mechanisms, allowing oncologists to switch to next-generation brain-penetrant inhibitors or rational drug combinations.

A comprehensive clinical overview of oncogenic driver alterations (EGFR, ALK, BRAF, KRAS G12C, HER2), small molecule kinase inhibitors, synthetic lethality, and liquid biopsy monitoring.

80+

FDA Approved Targeted Drugs

500+

Actionable Gene Alterations

3-5x

PFS Improvement vs Chemo

1,500+

Targeted Clinical Trials

Principles of Molecularly Targeted Oncology

Targeted cancer therapies are drugs designed to interfere with specific molecular entities and pathways necessary for tumor growth, invasion, and vascularization. Unlike cytotoxic chemotherapeutics that disrupt fundamental cell division processes across all proliferative tissues, targeted therapies exploit cancer-specific biochemical dependencies (often termed "oncogene addiction").

The paradigm of modern oncology mandates comprehensive genomic profiling (CGP) via tissue Next-Generation Sequencing (NGS) or circulating tumor DNA (ctDNA liquid biopsy) prior to therapy initiation to pinpoint actionable target mutations.

Major Classes of Targeted Compounds

Tyrosine Kinase Inhibitors (TKIs)

Small molecule oral agents targeting enzymatic kinase domains. Examples include 3rd-generation CNS-penetrant Osimertinib (EGFR), Alectinib / Lorlatinib (ALK), and Sotorasib / Adagrasib (KRAS G12C).

PARP Inhibitors (Synthetic Lethality)

Compounds including Olaparib, Rucaparib, and Talazoparib. Specifically trap PARP1 on DNA in homologous recombination-deficient (HRD / BRCA1/2) ovarian, breast, prostate, and pancreatic carcinomas.

Monoclonal Antibodies & Angiogenesis

Extracellular receptor inhibitors such as Cetuximab (EGFR), Trastuzumab (HER2), and vascular endothelial growth factor (VEGF) blockers like Bevacizumab that starve tumors of blood supply.

Tissue-Agnostic TRK & RET Inhibitors

Selective agents including Larotrectinib / Entrectinib (NTRK fusions) and Selpercatinib (RET) that demonstrate dramatic clinical efficacy regardless of primary tumor histology.

Actionable Biomarkers & Targeted Therapies

Gene Alteration	Associated Tumor Types	Standard Targeted Therapies	Diagnostic Testing Method
EGFR (Exon 19 del, L858R, T790M)	Non-Small Cell Lung Cancer (NSCLC)	Osimertinib, Gefitinib, Erlotinib, Amivantamab	NGS / Droplet Digital PCR
ALK Translocations / Fusions	NSCLC (~5% of adenocarcinoma)	Alectinib, Brigatinib, Lorlatinib	FISH / NGS RNA Fusion Panel
KRAS G12C	NSCLC, Colorectal, Pancreatic	Sotorasib, Adagrasib	Tissue / ctDNA NGS
BRAF V600E / V600K	Melanoma, NSCLC, Colorectal, Thyroid	Dabrafenib + Trametinib, Encorafenib	PCR / NGS
BRCA1 / BRCA2 (HRD)	Ovarian, Breast, Prostate, Pancreatic	Olaparib, Talazoparib, Niraparib	Germline & Somatic Sequencing
HER2 (ERBB2 Amplification)	Breast, Gastric, Colorectal, Salivary	Trastuzumab, Pertuzumab, Tucatinib, T-DXd	IHC & Dual-In-Situ Hybridization

Frequently Asked Questions (Clinical FAQ)

What is targeted therapy and how is it different from chemotherapy?

Targeted therapy acts on specific molecular switches, mutated proteins, or aberrant genes that control tumor cell survival. Chemotherapy is cytotoxic to all rapidly multiplying cells. Because targeted drugs zero in on tumor-specific genetic vulnerabilities, they spare many healthy cells and offer higher tumor selectivity.

Why is Next-Generation Sequencing (NGS) required before starting targeted therapy?

Targeted drugs are precision tools that work exclusively in tumors expressing the specific matching gene mutation or fusion. Comprehensive Genomic Profiling through tissue NGS or blood-based liquid biopsy (ctDNA) is necessary to determine which targeted drug or clinical trial will be clinically effective.

What are Tyrosine Kinase Inhibitors (TKIs)?

TKIs are small molecule medications (most taken orally) that penetrate cell membranes to block intracellular kinase enzyme domains. They interrupt oncogenic cascade signals like MAPK/ERK and PI3K/AKT, stopping cell division and inducing apoptosis.

How do PARP inhibitors work against BRCA-mutated tumors?

PARP inhibitors utilize the principle of 'synthetic lethality.' In cancer cells with defective homologous recombination DNA repair (due to BRCA1/2 mutations), inhibiting PARP prevents base-excision repair of single-strand breaks. This causes accumulation of lethal double-strand breaks that normal, repair-proficient cells can withstand.

How is acquired drug resistance managed in targeted oncology?

Cancers frequently develop secondary resistance mutations (e.g., EGFR C797S) or activate bypass signaling loops. Oncologists use serial liquid biopsies (ctDNA) to detect resistance mutations early and switch to next-generation brain-penetrant inhibitors, antibody-drug conjugates, or combination regimens.

Clinically Reviewed by Dr. Elena Rostova, MD, PhD

Director of Molecular Oncology & Precision Therapeutics • ONCorg Genomics Working Group

Clinical review updated August 2026. Aligned with ESMO and NCCN Precision Oncology Biomarker Testing Guidelines.