What is Ontruzant® ? (trastuzumab-dttb)

The U.S. Food and Drug Administration (FDA) has approved Ontruzant (trastuzumab-dttb), a biosimilar to Herceptin (trastuzumab) for treatment of 3 different cancers. It is the third trastuzumab biosimilar to be approved for effectiveness across all eligible indications: treatment of certain patients with HER2+ early breast cancer, metastatic breast cancer and metastatic gastric cancer or gastroesophageal junction adenocarcinoma. HER2+ cancer is characterized by tumors that overproduce a specific molecule known as human epidermal growth factor receptor-2, or HER2.


Biosimilars are biological products that are highly similar to a previously approved biological product. The originally approved agents are called reference products. To gain approval, biosimilars can have no clinically meaningful differences from the reference products in either effectiveness or safety. Only minor differences in the inactive components are permitted in biosimilar products.

Biosimilars are intended to be lower cost, high-quality treatment options.2 Biosimilars match indication, dosing regimen, strength, dosage form, and route of administration, and may be legally manufactured after the original product’s patent expires.1

More on this topic

Ontruzant is manufactured by Samsung Bioepis, a Korean biopharmaceutical company started in 2012. It is the third biosimilar to trastuzumab (also known by the brand Herceptin by Genentech) to receive regulatory approval in the United States.3 A joint venture between Samsung BioLogics and Biogen, the company has invested in a pipeline of biosimilar drugs covering a wide range of therapeutic areas including oncology and immunology. The drug is marketed and distributed in the US by Merck.2

Approval based on research

Ontruzant is part of a chemotherapy regimen. Its FDA approval is based on data from 7 clinical trials that resulted in similar safety and survival outcomes between Ontruzant and Herceptin (trastuzumab). This yielded an equivalent rate of pathologic complete response.4

The European Commission approved Ontruzant in November 2017 and it has been used effectively in numerous European countries.2,4

Fighting Breast Cancer

Ontruzant is indicated for the treatment of different kinds of breast cancer including adjuvant treatment of HER2-overexpressing early breast cancer. Adjuvant therapy attempts to keep cancer from recurring after initial treatment, like surgery. Ontruzant is just one component of an adjuvant treatment regimen that includes other chemotherapy agents dependent on individual diagnosis. Ontruzant may also be used to treat HER2+ metastatic breast cancer, which is breast cancer that has already spread to other parts of the body.

How Ontruzant works

Ontruzant is used when the tumor has been tested to show the overexpression HER2. This means that cancer produces an excessive amount of the HER2 protein on the surface of the tumor cells, accelerating their growth.1 HER2 is overexpressed in about a quarter of breast cancers and a fifth of gastric cancers. Ontruzant inhibits the proliferation of the tumor cells that overexpress HER2.

Ontruzant is administered over specific dosing schedules as determined by an oncologist based on diagnosis and body weight, as well as by other drugs being used in the regimen. These vary based on individual conditions.1

Possible side effects of Ontruzant

According to the FDA, the most common side effects of Ontruzant in breast cancer include fever, nausea, vomiting, infusion reactions, diarrhea, infections, increased cough, headache, fatigue, shortness of breath, rash, lowered amounts of certain white blood cells, lowered red blood cells, and muscle pain.2 This is not an exhaustive list of all potential side effects of Ontruzant. Talk to your doctor or pharmacist for further information. As when starting any new drug, before starting treatment with Ontruzant, patients should talk to their doctor about all their health conditions as well as any medications (prescription and over-the-counter), vitamins, and herbal supplements they are taking. Some medications or supplements may interfere with each other and may cause side effects.

Some people experience infusion reactions. These can be managed by decreasing the rate of infusion or stopping infusion, dependent on the severity of the reaction. Infusions must always be administered under medical supervision.1

Important things to know about Ontruzant

Serious cardiac function warnings have been associated with Ontruzant treatment including the risk of left ventricular cardiac dysfunction. A thorough cardiac assessment, including history, physical exam, and echocardiogram or MUGA scan should be conducted prior to and during treatment. Women of reproductive age should determine their pregnancy status before beginning treatment. These products can cause fetal harm when administered to a pregnant woman. Women who can become pregnant who receive Ontruzant should use birth control during their treatment and for seven months after treatment with Ontruzant is completed (patients should discuss appropriate birth control methods with their doctor).1

Patients should talk to their doctor if they have any questions, or if they have questions regarding their Ontruzant regimen.

By providing your email address, you are agreeing to our privacy policy. We never sell or share your email address.

Written by: Emily Downward | Last reviewed: October 2020.