Loncastuximab tesirine is used to treat large B-cell lymphoma after at least two other cancer treatments did not work or have stopped working.

Loncastuximab tesirine may also be used for purposes not listed in this medication guide.

Tell your doctor if you have ever had:

• liver problems; or
• an infection.

Loncastuximab tesirine can harm an unborn baby if the mother or the father is using this medicine.

• If you are a woman, you may need a pregnancy test to make sure you are not pregnant. Use birth control while using this medicine and for at least 9 months after your last dose.
• If you are a man, use birth control if your sex partner is able to get pregnant. Keep using birth control for at least 6 months after your last dose.
• Tell your doctor right away if a pregnancy occurs.

It may be harder for a man to get a woman pregnant while using this medicine. You should still use birth control to prevent pregnancy because the medicine can harm an unborn baby.

Do not breastfeed while using this medicine, and for at least 3 months after your last dose.

Use Loncastuximab Tesirine (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:

• new or worsening skin rash, peeling, redness, or irritation;
• new or worsening swelling, weight gain, chest pain, shortness of breath, or trouble breathing;
• fluid build-up in or around the lungs--pain when you breathe, feeling short of breath while lying down, wheezing, gasping for breath, cough with foamy mucus, cold and clammy skin, anxiety, rapid heartbeats;
• low blood cell counts--fever, chills, tiredness, mouth sores, skin sores, easy bruising, unusual bleeding, pale skin, cold hands and feet, feeling light-headed or short of breath; or
• signs of a serious infection--flu symptoms, cough, weakness, body aches, headache, trouble breathing, or skin wounds with pain, redness, warmth, or swelling.

Common side effects may include:

• tiredness or weakness;
• rash;
• swelling;
• nausea;
• muscle or joint pain;
• increase in blood sugar; or
• changes in blood or lab tests.

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.

Loncastuximab tesirine could make you sunburn more easily. Avoid sunlight or tanning beds. Wear protective clothing and use sunscreen (SPF 30 or higher) when you are outdoors.