What is Lapatinib used for?

HER2 positive breast cancer that has spread, given with capecitabine; hormone receptor positive, HER2 positive breast cancer that has spread, given with letrozole.

What are the common side effects of Lapatinib?

Diarrhea. Redness, soreness, peeling, or blisters on the palms of your hands or soles of your feet. Feeling sick to your stomach or throwing up. Rash or dry skin. Feeling tired or weak. Mouth sores.

When should I call my care team while taking Lapatinib?

Yellow skin or eyes, dark tea colored urine, or pain on the right side of your belly; Shortness of breath, swelling in your legs, or a racing or uneven heartbeat; Diarrhea that does not get better with the medicine your team gave you, or more than 4 to 6 loose stools in a day; New or worse cough, chest pain, or trouble breathing; A rash with blisters, peeling skin, or sores in your mouth or eyes; Feeling faint or passing out.

Lapatinib

Say it: la-PA-tih-nib · Brand names: Tykerb

Lapatinib is a targeted therapy pill that blocks HER2, a protein that helps some breast cancers grow.

What it is

Some breast cancer cells have too much of a protein called HER2. HER2 sends signals that tell cells to grow. Lapatinib blocks these signals from inside the cell, which can slow the cancer.

Often used for

HER2 positive breast cancer that has spread, given with capecitabine
hormone receptor positive, HER2 positive breast cancer that has spread, given with letrozole

How you get it

Lapatinib is a pill you take by mouth at home, once a day. Take it on an empty stomach, at least 1 hour before or 1 hour after a meal. Your schedule may be different.

Common side effects and what helps

Diarrhea. Drink plenty of fluids. Tell your team early, since they may give you medicine to help.
Redness, soreness, peeling, or blisters on the palms of your hands or soles of your feet. Use thick lotion, wear soft shoes, and avoid hot water.
Feeling sick to your stomach or throwing up. Eat small meals and ask your team about anti-nausea medicine.
Rash or dry skin. Use gentle soap and fragrance free lotion.
Feeling tired or weak. Rest when you need to, and try short walks.
Mouth sores. Brush gently with a soft toothbrush and rinse with a mild salt water rinse. Avoid spicy foods.

Call your care team right away if you have

Yellow skin or eyes, dark tea colored urine, or pain on the right side of your belly
Shortness of breath, swelling in your legs, or a racing or uneven heartbeat
Diarrhea that does not get better with the medicine your team gave you, or more than 4 to 6 loose stools in a day
New or worse cough, chest pain, or trouble breathing
A rash with blisters, peeling skin, or sores in your mouth or eyes
Feeling faint or passing out

Before you start, tell your team

If you are pregnant, may become pregnant, or are breastfeeding
If you have heart problems, including an uneven heartbeat
If you have liver problems
All the medicines, vitamins, and herbal products you take, since some can change how this medicine works

Good to know

This medicine can cause serious liver damage. You will have blood tests to check your liver.
It can weaken the heart's pumping. You will have heart tests before and during treatment.
It can change your heart rhythm. You may have heart tracings (ECGs) and blood tests for body salts.
Rarely, it can cause lung inflammation or a serious skin reaction.

At home

Take all the pills for one dose at the same time each day, on an empty stomach.
Do not eat grapefruit or drink grapefruit juice while taking this medicine.
If you miss a dose or throw up after taking it, ask your team what to do. Do not take extra pills to make up for it.
Store the pills at room temperature in the original bottle, away from children and pets.

Questions to ask

How long will I take this medicine?
What heart tests will I need?
What should I do at the first sign of diarrhea?
Which side effects should I call about right away, and which can wait until my next visit?

Side effect guides

Sources

Quick answers

What is Lapatinib?: Lapatinib is a targeted therapy pill that blocks HER2, a protein that helps some breast cancers grow. Brand names: Tykerb.
What is Lapatinib used for?: HER2 positive breast cancer that has spread, given with capecitabine; hormone receptor positive, HER2 positive breast cancer that has spread, given with letrozole.
How is Lapatinib given?: Lapatinib is a pill you take by mouth at home, once a day. Take it on an empty stomach, at least 1 hour before or 1 hour after a meal. Your schedule may be different.
What are the common side effects of Lapatinib?: Diarrhea. Redness, soreness, peeling, or blisters on the palms of your hands or soles of your feet. Feeling sick to your stomach or throwing up. Rash or dry skin. Feeling tired or weak. Mouth sores.
When should I call my care team while taking Lapatinib?: Yellow skin or eyes, dark tea colored urine, or pain on the right side of your belly; Shortness of breath, swelling in your legs, or a racing or uneven heartbeat; Diarrhea that does not get better with the medicine your team gave you, or more than 4 to 6 loose stools in a day; New or worse cough, chest pain, or trouble breathing; A rash with blisters, peeling skin, or sores in your mouth or eyes; Feeling faint or passing out.

Last updated: 2026-10-27. Medically reviewed by Veli Bakalov, MD, medical oncologist (October 2026). General education from Step by Step, the patient portal of HemeOncBuddy.