Erlotinib – Targeted Therapy

Erlotinib is a potent antineoplastic agent belonging to the class of epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors. The drug is a highly selective low-molecular-weight inhibitor designed for targeted therapy of malignant neoplasms whose development is associated with the activation of the HER1/EGFR receptor signaling pathways.

The mechanism of action of erlotinib is based on competitive inhibition of adenosine triphosphate (ATP) binding to the intracellular tyrosine kinase domain of the EGFR receptor. This blocks receptor autophosphorylation and interrupts downstream signaling cascades responsible for cell proliferation, angiogenesis, and tumor survival. The drug is particularly effective in the presence of specific activating mutations in the EGFR gene (exon 19 deletions or L858R substitution in exon 21).

Erlotinib exhibits high bioavailability when administered orally. The systemic effect of the drug allows for efficient suppression of tumor cell growth and the induction of apoptosis, leading to disease stabilization and increased progression-free survival in patients with metastatic forms of cancer.

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Indications

Erlotinib is used for the treatment of solid tumors with confirmed molecular genetic status:

Non-Small Cell Lung Cancer (NSCLC): as first-line therapy and maintenance therapy in patients with locally advanced or metastatic disease harboring activating EGFR mutations.
Pancreatic Cancer: in combination with gemcitabine for the first-line treatment of patients with metastatic pancreatic adenocarcinoma.
Advanced NSCLC: as second- or third-line therapy after the failure of at least one prior standard chemotherapy regimen.
The drug may be prescribed as maintenance treatment for patients with stable disease following four cycles of standard first-line platinum-based chemotherapy.

Dosage and administration

Erlotinib therapy requires constant supervision by an oncologist and adherence to a strict dosing regimen in tablet form.

In Lung Cancer (NSCLC): the standard dose is 150 mg once daily.
In Pancreatic Cancer: the recommended dose is 100 mg once daily in combination with intravenous gemcitabine.
Administration Rules: the drug must be taken strictly on an empty stomach — at least 1 hour before or 2 hours after food intake. Food significantly increases bioavailability, which may lead to unpredictable toxicity.
Lifestyle Factors: smoking significantly reduces plasma concentrations of erlotinib (by 50–60%) through the induction of metabolic enzymes; therefore, patients are strongly advised to stop smoking.
Dose Adjustment: if severe side effects or pronounced skin rash develop, the dose is reduced stepwise (by 50 mg) or treatment is temporarily interrupted.

The use of erlotinib is restricted or prohibited under the following clinical conditions:

Hypersensitivity: presence of severe allergic reactions to erlotinib or any of the excipients in the medication.
Pregnancy and Lactation: the drug has fetotoxic effects. Women of childbearing potential must use reliable contraception during treatment and for 2 weeks after its completion.
Severe Hepatic Impairment: (Child-Pugh Class C), as erlotinib is primarily metabolized in the liver.
Severe Renal Impairment: due to limited safety data in patients with a creatinine clearance of less than 15 ml/min.
Pediatric Use: safety and efficacy in children and adolescents under 18 years of age have not been established.

The safety profile of erlotinib is characterized by specific targeted reactions requiring symptomatic management:

Dermatologic Reactions: acne-like rash (observed in more than 75% of patients), dry skin, pruritus, and paronychia (inflammation of the nail fold).
Gastrointestinal Tract: diarrhea (often severe, leading to dehydration), nausea, vomiting, and stomatitis.
Respiratory System: in rare cases (approx. 1%), interstitial lung disease (ILD) may develop, requiring immediate discontinuation of the drug.
Ocular Symptoms: keratitis, conjunctivitis, pronounced dry eyes, and the risk of corneal ulceration.
Laboratory Parameters: increased levels of liver transaminases and bilirubin, necessitating regular biochemical blood analysis.

Frequently Asked Questions

Erlotinib is a targeted anticancer substance, an EGFR (epidermal growth factor receptor) tyrosine kinase inhibitor. It works by blocking signaling pathways inside the cancer cell that stimulate its growth and proliferation. This results in the suppression of tumor development and, in some cases, tumor shrinkage.

Erlotinib is primarily used for the treatment of advanced non-small cell lung cancer (NSCLC), specifically in patients whose tumors have certain EGFR mutations. It is also used in combination with other agents to treat metastatic pancreatic cancer.

Erlotinib is significantly more effective in patients whose tumor cells harbor specific EGFR mutations (e.g., exon 19 deletions or L858R mutations). Genetic testing allows the physician to determine if the tumor is likely to respond to the active substance, helping to avoid ineffective therapy.

Erlotinib is taken orally in tablet form. It is crucial to take it on an empty stomach—at least 1 hour before or 2 hours after food. Taking the medication with food can unpredictably increase its concentration in the bloodstream, raising the risk of severe side effects.

Smoking significantly accelerates the metabolism of erlotinib, lowering its concentration in the blood and reducing overall treatment efficacy. Additionally, drugs that reduce stomach acid (such as PPIs or antacids) can interfere with erlotinib's dissolution and absorption. Several hours should separate the intake of antacids and erlotinib.

Similar to other EGFR inhibitors, an acne-like rash is a common side effect (occurring in about 75% of patients). Since EGFR is present in normal skin cells, erlotinib affects them as well. Clinically, the presence and severity of the rash often correlate with a better therapeutic response from the tumor.