Formosa Pharmaceuticals Files EU Application for Trastuzumab Emtansine Biosimilar TSY-110

Formosa Pharmaceuticals has submitted a clinical trial application (CTA) to European regulators to conduct a pivotal trial of TSY-110, a proposed biosimilar to Roche's ado-trastuzumab emtansine (Kadcyla), an antibody-drug conjugate (ADC) for treating HER2-positive breast cancer, the company announced August 28, 2026.¹ TSY-110, also designated EG12043, is being co-developed with Taiwan-based EirGenix and is positioned to become the first biosimilar alternative to Roche’s ADC in major regulated markets, according to Formosa Pharmaceuticals.¹

"Filing this CTA marks a significant achievement for Formosa Pharmaceuticals and underscores our strategic alliance with EirGenix," said Erick Co, PhD, president and CEO of Formosa Pharmaceuticals, in a press release.¹ "Antibody-drug conjugates have established themselves as mainstays in oncology, including HER2-positive breast cancer care, but patient access remains constrained by high treatment costs. Advancing TSY-110 into clinical evaluation is a momentous step toward fulfilling our goal of delivering world-class, accessible ADC options to oncologists and patients."

The upcoming pivotal trial, designed following guidance from both US and EU regulatory authorities, will assess the safety, tolerability, pharmacokinetics, and immunogenicity of TSY-110 compared with the reference product. TSY-110 links the HER2-targeting monoclonal antibody trastuzumab to the cytotoxic payload mertansine, designed to selectively eliminate HER2-overexpressing cancer cells while limiting systemic toxicity. Formosa Pharmaceuticals said comprehensive preclinical assessments have demonstrated high biosimilarity, consistent drug-antibody ratio, and comparable plasma kinetics to the reference product.¹

Why is a biosimilar alternative to trastuzumab emtansine significant?

Trastuzumab emtansine was first approved by the FDA in 2013 for HER2-positive metastatic breast cancer and later gained an additional early-stage breast cancer indication in 2019, supported by the phase 3 KATHERINE trial, which showed the drug significantly reduced the risk of invasive disease recurrence or death compared with trastuzumab alone in patients with residual disease after neoadjuvant therapy.² HER2-positive disease affects an estimated 360,000 to 480,000 of the roughly 2.4 million breast cancer cases diagnosed globally in 2024, based on a standard prevalence rate of 15% to 20%.¹ Under the Kadcyla brand, trastuzumab emtansine generated approximately $2.5 billion in global sales in 2025.¹

How does this fit into the Formosa Pharmaceuticals–EirGenix partnership?

Formosa Pharmaceuticals and EirGenix first established their co-development alliance for TSY-0110 (EG12043) in March 2022, under which Formosa Pharmaceuticals is eligible to receive up to $30 million in upfront and milestone payments from EirGenix in exchange for profit-sharing rights. Under the deal, EirGenix supplies its own trastuzumab (Herceptin; Roche) biosimilar, EG12014, as a key intermediate in TSY-110's manufacturing.³

EirGenix's EG12014 has been developed in partnership with Sandoz and was under regulatory review in the United States and European Union following biologics license application and marketing authorization submissions in December 2021.³ Formosa Pharmaceuticals’ pipeline also includes APP13007, an FDA-approved treatment for post-surgical ocular inflammation and pain built on the company's proprietary APNT nanoparticle formulation platform, alongside a broader portfolio of biosimilar and novel oncology assets.¹

What are the limitations?

A CTA filing authorizes the start of clinical testing and does not indicate that TSY-110 has demonstrated biosimilarity in humans. The pivotal trial has not yet begun, and no timeline for potential approval or launch was disclosed.

References

1. Formosa Pharmaceuticals. Formosa Pharmaceuticals files clinical trial application for TSY-110, an antibody-drug conjugate biosimilar targeting HER2-positive breast cancers. Press release. Published August 28, 2026. Accessed August 28, 2026. https://www.formosapharma.com/formosa-pharmaceuticals-files-clinical-trial-application-for-tsy-110-an-antibody-drug-conjugate-biosimilar-targeting-her2-positive-breast-cancers/
2. von Minckwitz G, Huang CS, Mano MS, et al. Trastuzumab emtansine for residual invasive HER2-positive breast cancer. N Engl J Med. 2019;380(7):617-628. doi:10.1056/NEJMoa1814017
3. Formosa Pharmaceuticals. Formosa Pharmaceuticals and EirGenix establish a co-development alliance to develop TSY-0110/EG12043 (ado-trastuzumab emtansine biosimilar) for HER2-positive breast cancer. Press release. Published March 24, 2022. Accessed August 28, 2026. https://www.formosapharma.com/formosa-pharmaceuticals-and-eirgenix-establish-a-co-development-alliance-to-develop-tsy-0110-eg12043-ado-trastuzumab-emtansine-biosimilar-for-her2-positive-breast-cancer/