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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. Also known as SB3, it is the third biosimilar to be approved for effectiveness across all eligible indications: treatment of HER2-overexpressing breast cancer, metastatic breast cancer and metastatic gastric cancer or gastroesophageal junction adenocarcinoma in patients who have not received prior treatment for metastatic disease.


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

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 will be 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 SB3 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 node-positive or node-negative breast cancer. An adjuvant enhances the effectiveness of other medical treatments. Ontruzant is just one component of a treatment regimen that includes other chemotherapy agents dependent on individual diagnosis.

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 condition. If a dose is missed by one week or less, the dose should be administered as soon as possible. If the time lapse is more than one week, a reloading dose is generally required.1

Possible side effects of Ontruzant

According to the FDA, the most common side effects of Ontruzant in breast cancer are fever, nausea, vomiting, infusion reactions, diarrhea, infections, increased cough, headache, fatigue, dyspnea, rash, neutropenia, anemia, and myalgia.2 This is not a complete list of all possible side effects of Ontruzant. As when starting any new drug, discuss with your doctor in advance all medications, supplements and vitamins you take.

Some people experience infusion site 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. Effective contraception should be used during treatment and for 7 months following the last dose of Ontruzant, which is the period it takes to fully wash out of the system.1

Written by: Emily Downward | Last reviewed: October 2019.
  1. ONTRUZANT prescribing information available at: Accessed 1/26/19.
  2. US FDA Approves ONTRUZANT® (trastuzumab-dttb), Samsung Bioepis’ First Oncology Medicine in the United States. Available at: Accessed 1.26.19.
  3. FDA approves Ontruzant, biosimilar to Herceptin, for breast and gastric cancers. Available at: cancer/news/online/%7B1ba03140-a3bb-491e-a50e-74fa4b7bedc3%7D/fda-approves-ontruzant-biosimilar-to-herceptin-for-breast-and-gastric-cancers. Accessed 1.26.19.
  4. FDA Approves Third Trastuzumab Biosimilar. Available at: Accessed 1.25.19.
  5. Ontruzant. Avaialable at: Accessed 1.26.19.