Nick Mulcahy

December 13, 2013

SAN ANTONIO — As the epoch-making breast cancer targeted therapy trastuzumab (Herceptin, Genentech) is coming to the end of its patent protection, a new kind of knock-off product is being developed to compete in the drug's large market.

The patent on Herceptin expires in 2014 in Europe and in 2019 in the United States, Genentech spokesperson Susan Wilson told Medscape Medical News in an email.

Would-be competing therapies are in development in at least 2 countries — the United States and China — and one has already been approved in India, as reported by Medscape Medical News.

However, these agents are not generics. They belong to a product category known as biosimilars, which reflects their contents, explained Charles Zacharchuk, MD, PhD, development lead at Pfizer Worldwide Research and Development.

Generics are chemically synthesized small-molecule drugs. However, trastuzumab, which is a monoclonal antibody, is a biologic, and thus is a unique large-molecule drug. Both the original biologic drug and the biosimilar are produced in living cells. The manufacturing is complex and subject to the lack of uniformity in nature. "There will be variability," Dr. Zacharchuk told Medscape Medical News here at the 36th Annual San Antonio Breast Cancer Symposium.

There are currently no approved biosimilars in the United States, but Pfizer is working to change that.

Dr. Zacharchuk presented a poster on the trial design of a 600-patient phase 3 study of patients with HER2-positive metastatic breast cancer that compares Pfizer's trastuzumab biosimilar candidate (PF-05280014) with the original, trastuzumab. Patients in both groups will also be treated with paclitaxel.

The primary goal of the study is to demonstrate the similarity in objective response rate of the 2 agents. Secondary end points include safety measures and progression-free survival.

Trastuzumab remains a very important drug in breast cancer, despite the approval of a number of other drugs — such as pertuzumab (Perjeta, Genentech) and ado-trastuzumab emtansine (TDM-1, Kadcyla; Genentech) — for the treatment of HER2-positive disease, said Aditya Bardia, MD, a medical oncologist at the Massachusetts General Hospital Cancer Center in Boston.

"Trastuzumab is the mainstay of treatment for HER2-positive disease," he told Medscape Medical News.

Dr. Bardia explained that trastuzumab, in combination with chemotherapy, continues to be the only approved targeted therapy for the adjuvant treatment of local HER2-positive disease. Although pertuzumab is now approved for neoadjuvant use in localized disease and for metastatic disease, it must always be used in combination with trastuzumab. TDM-1 is only approved for metastatic disease.

"It's difficult to know what could or might replace trastuzumab," said Dr. Bardia, referring to its dominant status in this breast cancer type. TDM-1 is a candidate, but trials comparing it with trastuzumab are ongoing, he explained.

Dr. Zacharchuk hopes that a Pfizer trastuzumab biosimilar will result in even more women receiving targeted therapy. "One of the major limitations to access is price," he said. Currently in the United States, treatment with this drug costs around $4500 per month.

"We hope to provide a high-quality lower-cost alternative," he said, adding that "trastuzumab is likely to remain important, especially globally."

There could be competition. Mylan, the Indian company that is now marketing its trastuzumab biosimilar under the trade name Hertraz in India, has exclusive commercialization rights to the product in Australia, Canada, the European Union, Japan, New Zealand, and the United States, and in European Free Trade Association countries.

Dr. Zacharchuk is an employee of Pfizer.

36th Annual San Antonio Breast Cancer Symposium (SABCS): Abstract OT1-1-01. Presented December 11, 2013.

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