Biogen is suspected of reserving a test for patients on natalizumab to Tysabri® users only and refusing to make the test available to patients on other natalizumab based medicines such as Tyruko® of Sandoz, a biosimilar version of reference product Tysabri®. According to ACM, if this is true and if Biogen is not able to offer a solid explanation for the bundling of medicinal treatment and test, Biogen could be found to be in breach of Article 102, Treaty on the Functioning of the European Union, which prohibits the abuse of a dominant position on the relevant market.

Patients treated with natalizumab must be regularly tested for the risk of developing progressive multifocal leukoencephalopathy (PML), an infection caused by the JC-virus (JCV), which may be fatal or result in severe disability. Biogen developed the Stratify diagnostic which tests for the presence of anti-JCV antibodies and provides it free of charge to patients receiving Biogen’s Tysabri®. For its part, Sandoz also supplies a diagnostic, called ImmunoWell, to patients free of charge to test for the risk of PML. However, healthcare professionals seem to prefer Stratify over ImmunoWell as the former was developed on the basis of more than 15 years of data which is far in excess of the data supporting ImmunoWell.

The Dutch investigation mirrors a case which the Autorità Garante della Concorrenza e del Mercato, the Italian competition authority (AGCM),opened against Biogen on 27 May 2026 (see, Van Bael & Bellis Life Sciences News & Insights, 29 May 2026). Like AGCM, ACM will now inquire whether Biogen engaged in an illegitimate form of bundling that would allow it to leverage its market power derived from its Stratify diagnostic to protect its sales of Tysabri® and hinder competition from Sandoz’s Tyruko®.  If ACM finds fault with Biogen’s behaviour, this will be a new example of approaches adopted by specific marketing authorisation holders of biological medicines to impede, delay or slow down the market entry of biosimilar rivals.