Fam-trastuzumab deruxtecan is used in adults to treat HER2-positive breast cancer that has spread to other parts of the body (metastatic) or cannot be removed with surgery.

Fam-trastuzumab deruxtecan is also used in adults who have received an anti-HER2 breast cancer treatment before for metastatic diseases, or have breast cancer that has come back within 6 months of completing treatment for early stages breast cancer.

Fam-trastuzumab deruxtecan can also used in adults to treat a certain type of HER2-positive esophageal cancer.

Fam-trastuzumab deruxtecan is usually given after other cancer treatments did not work or have stopped working.

Fam-trastuzumab deruxtecan may also be used for purposes not listed in this medication guide.

Tell your doctor if you have ever had:

• heart problems;
• breathing problems; or
• an infection.

You may need to have a negative pregnancy test before starting this treatment.

Fam-trastuzumab deruxtecan can harm an unborn baby if the mother or the father is using this medicine.

• If you are a woman, do not use fam-trastuzumab deruxtecan if you are pregnant. Use effective birth control to prevent pregnancy while you are using this medicine and for at least 7 months after your last dose.
• If you are a man, use effective birth control if your sex partner is able to get pregnant. Keep using birth control for at least 4 months after your last dose.
• Tell your doctor right away if a pregnancy occurs while either the mother or the father is using fam-trastuzumab deruxtecan.

This medicine may affect fertility (ability to have children), in men.

Do not breastfeed while using this medicine, and for at least 7 months after your last dose.

Use Fam-Trastuzumab Deruxtecan (Intravenous) exactly as directed on the label, or as prescribed by your doctor. Do not use in larger or smaller amounts or for longer than recommended.

Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have:

• chest tightness, wheezing, cough, new or worsening shortness of breath;
• pounding heartbeats or fluttering in your chest;
• fever, tiredness, dizziness;
• swelling in your lower legs, sudden weight gain;
• a light-headed feeling, like you might pass out;
• low blood cell counts--fever, chills, mouth sores, skin sores, easy bruising, unusual bleeding, pale skin, cold hands and feet; or
• low potassium level--leg cramps, constipation, irregular heartbeats, fluttering in your chest, increased thirst or urination, numbness or tingling, muscle weakness or limp feeling.

Your cancer treatments may be delayed or permanently discontinued if you have certain side effects.

Common side effects may include:

• nausea, vomiting, loss of appetite;
• diarrhea, constipation;
• cough;
• fever, feeling tired;
• low blood cell counts;
• low potassium;
• abnormal liver function tests; or
• hair loss.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Follow your doctor's instructions about any restrictions on food, beverages, or activity.