Devastating global burden. Lung cancer is the leading cause of cancer-related mortality worldwide, responsible for over 25% of all cancer deaths. Despite advances in diagnosis and treatment, the five-year survival rate remains stubbornly low, making the search for new therapeutic strategies an urgent priority.
Two main types guide treatment. Lung cancer is broadly divided into non-small cell lung cancer (NSCLC), which accounts for about 85% of cases, and small cell lung cancer (SCLC), comprising the remaining 15%. Each type has distinct molecular characteristics, risk factors, and treatment approaches.
Smoking and environmental causes. Cigarette smoke is responsible for over 80% of lung cancer cases, introducing carcinogens that damage DNA and activate mutations in key cancer-driving genes. Additional contributors include secondhand smoke, air pollution, radon gas, and occupational exposures to asbestos and arsenic.
Genetic drivers in non-smokers. Non-smokers can also develop lung cancer through genetic mutations such as EGFR (epidermal growth factor receptor) alterations and ALK gene rearrangements. These molecular changes are now key targets for precision therapies, shifting lung cancer treatment toward individualized approaches.
Adenocarcinoma: the most common subtype. Adenocarcinoma arises from glandular cells in the outer lung regions and is the most frequently diagnosed form of NSCLC. It is often found in non-smokers and younger individuals, and is strongly associated with EGFR, ALK, and KRAS genetic mutations - making it an ideal candidate for targeted therapies.
Squamous cell carcinoma and smoking. This subtype develops in the central airways near the bronchial tubes and is closely linked to smoking - accounting for roughly 80-90% of cases in men and women respectively. It grows more slowly than other subtypes but is still associated with significant morbidity.
Large cell carcinoma: aggressive and rare. The least common NSCLC subtype, large cell carcinoma can appear in any part of the lung and grows rapidly. Because it lacks the clear cellular features of the other subtypes, it presents significant diagnostic challenges and is typically identified after surgical removal rather than biopsy.
Small cell lung cancer: fast and invasive. SCLC is strongly linked to heavy smoking and grows very rapidly, with about 70% of patients already having distant metastases at the time of first diagnosis. It spreads most commonly to the brain, liver, and bones, making it one of the most aggressive cancers known.
What tyrosine kinases do. Tyrosine kinases (TKs) are a class of enzymes that control critical cell processes - including growth, differentiation, proliferation, and survival - by adding phosphate groups to specific proteins. In healthy cells, their activity is carefully regulated; when disrupted, they can drive cancer development.
How TKs become oncogenic. Mutations, overexpression, and abnormal stimulation can transform normal TKs into cancer-promoting engines. There are 90 TK genes in the human genome, split into receptor tyrosine kinases (RTKs) like EGFR and VEGFR, which sit on the cell surface, and non-receptor tyrosine kinases (NRTKs) like Src and JAK, which operate inside the cell.
EGFR: a pivotal target in NSCLC. The epidermal growth factor receptor (EGFR) plays a central role in NSCLC. Mutations in EGFR - particularly in exons 19 and 21 - cause the receptor to be permanently switched on, driving uncontrolled cell growth through downstream pathways like RAS-RAF-MEK-ERK and PI3K-AKT.
ALK and other key players. Beyond EGFR, rearrangements in the ALK gene and amplifications of FGFR also contribute to NSCLC by activating the same cancer-promoting pathways. These alterations all represent targets for modern precision medicines, and their detection through liquid biopsy and next-generation sequencing is improving patient outcomes.
How TKIs work. Tyrosine kinase inhibitors (TKIs) block cancer growth by competing with ATP for the binding site on TK enzymes, preventing the phosphorylation that would normally activate downstream cancer-promoting signals. This targeted approach can selectively shut down cancer cell proliferation while sparing normal cells.
Three generations of EGFR inhibitors. First-generation TKIs like gefitinib and erlotinib, and second-generation agents like afatinib, were major advances for EGFR-mutant NSCLC. However, a common resistance mutation called T790M in exon 20 limited their long-term effectiveness and drove development of further generations.
Third-generation: overcoming resistance. Osimertinib, a third-generation TKI, was specifically designed to target the T790M resistance mutation and has become the current standard of care for advanced EGFR-mutant NSCLC. It offers prolonged progression-free survival and is better tolerated than earlier agents.
ALK and other TKI targets. For NSCLC patients with ALK gene rearrangements, inhibitors like crizotinib, alectinib, and brigatinib have shown significant survival benefits. Clinical trials continue to explore novel TKIs targeting additional kinases such as ROS1, MET, and BRAF, expanding precision treatment options.
Two types of resistance. Drug resistance to TKIs can be intrinsic - where cancer cells never respond - or acquired, where cells initially respond but later develop resistance mechanisms. Acquired resistance is the more common problem, typically emerging after a median of 9 to 14 months of treatment in EGFR-mutant patients.
Resistance mechanisms are diverse. The most well-known acquired resistance mechanism is the T790M secondary mutation, which alters the kinase domain and reduces drug binding affinity. Additional mechanisms include activation of bypass signaling pathways, amplification of oncogenes like MET and HER2, and increased activity of drug efflux pumps.
Tumor heterogeneity complicates treatment. Lung cancers are highly variable between and within individual tumors. This intratumoral heterogeneity means that resistant subclones can emerge and expand during therapy, creating a moving target that is difficult to address with any single drug or drug combination.
Histological transformation adds complexity. A particularly challenging resistance mechanism is the transformation of NSCLC cells into SCLC-like cells during therapy. This phenotypic shift fundamentally changes the tumor's biology and requires completely different treatment strategies, demanding ongoing molecular monitoring throughout a patient's care.
A rich history of plant-based medicines. Plants have been used medicinally for thousands of years, and their secondary metabolites - compounds produced as part of the plant's own defense and signaling systems - have inspired many modern pharmaceuticals. These include anticancer medicines like paclitaxel (from yew bark) and doxorubicin.
Why natural products are attractive. Compared to synthetic compounds, naturally occurring phytochemicals are often more tolerable, less toxic, and available in forms that can be consumed orally. Nearly half of cancer patients in the United States report using dietary supplements after diagnosis, reflecting broad patient interest in natural approaches.
Mechanisms of anticancer action. Natural products can modulate cancer-related cell signaling, restore normal apoptosis (programmed cell death), and exert direct cytotoxic effects on tumor cells. Their ability to target multiple pathways simultaneously may help address the resistance mechanisms that limit conventional TKIs.
Adjuvant potential. Rather than replacing conventional treatments, natural products show particular promise as adjuvants - substances that enhance the effectiveness of existing therapies. In lung cancer specifically, several natural compounds have demonstrated synergistic effects when combined with TKIs, potentially helping to overcome drug resistance.
Alkaloids with EGFR-targeting activity. Capsaicin (from chili peppers) suppresses EGFR-mediated signaling cascades including FAK/Akt and p38 MAPK pathways, inhibiting tumor cell invasion and migration. Oxymatrine (from Sophora flavescens) blocks multiple EGFR pathways in gastric and glioma cancer cells, demonstrating broad anticancer potential.
Flavonoids: a versatile class. Flavonoids such as apigenin, baicalein, curcumin, and fisetin have all been shown to interfere with TK signaling. Apigenin inhibits EGFR phosphorylation and has synergistic effects when combined with gefitinib in TKI-resistant NSCLC. Baicalein inhibits Src tyrosine kinase and has demonstrated apoptosis induction in NSCLC cells.
Curcumin's multiple anti-NSCLC mechanisms. Curcumin, from the turmeric plant, has particularly impressive evidence in NSCLC. It enhances the effectiveness of gefitinib and erlotinib in resistant cells by reducing EGFR phosphorylation and accelerating EGFR degradation. Multiple clinical trials are underway exploring curcumin combined with EGFR-TKIs.
Polyphenols and terpenoids. Green tea's EGCG prevents EGFR-TK activation and has shown activity in erlotinib-resistant NSCLC cell lines. Resveratrol (found in grapes) and ginsenosides (from ginseng) target cell cycle regulation and cancer stem cell properties in NSCLC. Together, 67 recognized natural compounds have been identified as able to combat EGFR-TKI resistance through at least 30 distinct pathways.
The case for combining natural products with TKIs. The evidence reviewed in this paper supports the idea that combining plant-derived natural compounds with existing TKIs may enhance treatment efficacy and overcome resistance. These compounds can act as chemosensitizers, making cancer cells more responsive to drugs they would otherwise resist.
Multiple pathways targeted simultaneously. Natural compounds like curcumin, apigenin, and EGCG are particularly appealing because they can act on multiple cancer-promoting pathways at once - targeting EGFR, PI3K/AKT, NF-kB, and other networks simultaneously. This multi-target approach mirrors the complexity of cancer biology better than single-target drugs.
Clinical evidence is still emerging. While preclinical data (laboratory and animal studies) are compelling, robust clinical trial evidence for most natural compound and TKI combinations remains limited. Ongoing and planned trials for curcumin combined with gefitinib and erlotinib represent important steps toward clinical validation.
Need for rigorous future research. The authors emphasize that further preclinical and clinical studies are needed to establish the safety, efficacy, optimal dosing, and pharmacokinetic interactions of natural product and TKI combinations. Standardization of natural product preparations and patient selection criteria will also be critical for translating these findings into clinical practice.