Lapatinib (Tykerb) — Clinical FAQs

Question 1

What is Lapatinib FDA-approved to treat?

Accepted Answer

Lapatinib is FDA-approved for the following oncology indications: 1. Advanced or metastatic HER2-positive breast cancer — in combination with capecitabine, in patients who have received prior therapy including an anthracycline, a taxane, and trastuzumab 2. Hormone receptor-positive, HER2-positive metastatic breast cancer — in combination with letrozole in postmenopausal women for whom hormonal therapy is indicated (EGF30008 trial).

Question 2

How does Lapatinib work (mechanism of action)?

Accepted Answer

Lapatinib is a small-molecule, reversible dual inhibitor of the intracellular tyrosine kinase domains of both EGFR (HER1/ErbB1) and HER2 (ErbB2). By binding the ATP-binding cleft of these receptors in their inactive conformations, lapatinib prevents receptor autophosphorylation and activation of downstream oncogenic signaling through the PI3K/AKT/mTOR and RAS/RAF/MEK/ERK pathways, resulting in inhibition of cellular proliferation and induction of apoptosis in HER2-overexpressing tumor cells. As a small molecule, lapatinib crosses the blood-brain barrier more readily than antibody-based HER2-targeted therapies, conferring activity against CNS metastases. Unlike trastuzumab (which targets the extracellular domain), lapatinib acts intracellularly and retains activity against the truncated p95-HER2 receptor isoform that lacks the trastuzumab-binding domain — an important mechanism of trastuzumab resistance. Concurrent EGFR inhibition contributes to lapatinib's characteristic acneiform rash and diarrhea toxicity profile.

Question 3

How is Lapatinib administered?

Accepted Answer

Lapatinib is administered Oral (PO). Administer on an empty stomach: at least 1 hour before or 1 hour after a meal.

Question 4

What are the most common side effects of Lapatinib?

Accepted Answer

The most commonly reported side effects of Lapatinib (≥10% incidence) include: Diarrhea (>60%; Grade 3 in ~12–14%), Palmar-plantar erythrodysesthesia / hand-foot syndrome (with capecitabine; ~53%), Nausea, Rash / acneiform dermatitis (EGFR-mediated; face, trunk, scalp; ~28%), Fatigue / asthenia and others (13 total). Consult your oncologist for complete prescribing information.

Question 5

Does Lapatinib have a black box warning?

Accepted Answer

Yes. Lapatinib carries FDA black box warning(s) regarding: 1. Hepatotoxicity: Severe drug-induced liver injury, including fatal cases, has been reported in patients receiving lapatinib. Liver function tests (ALT, AST, total bilirubin) must be monitored before initiation, every 4–6 weeks during the first 6 months, and periodically thereafter. Permanently discontinue for Grade 3 or greater hepatotoxicity (ALT or AST >5× ULN or bilirubin >3× ULN). Patients carrying HLA-DQA1*02:01 and HLA-DRB1*07:01 alleles have approximately 9-fold increased risk of clinically significant hepatotoxicity.

Question 6

Is Lapatinib safe during pregnancy?

Accepted Answer

Lapatinib pregnancy safety: Category D — Lapatinib causes fetal harm based on its mechanism of action (HER2/EGFR signaling is critical for normal fetal cardiac and neurological development) and animal reproductive toxicology studies. Females of reproductive potential must use effective contraception during therapy and for at least 1 week after the final dose.. Oncologists should review the complete prescribing information and discuss reproductive risks with patients before initiating therapy.

Lapatinib — Drug Monograph

Mechanism of Action

FDA Indications

Common Side Effects

Clinical Pearl

Related Therapies & Mechanisms