Defining Your Patient Group – A Cautionary Tale

The recent EPO appeal decision T0589/22 discusses the requirement of plausibility in a diagnostic method case, but also provides a cautionary tale regarding defining a patient group in a claim.

At the European Patent Office, for a therapeutic application (and by extension, a diagnostic application) to be considered sufficiently disclosed, the patent application and/or the common general knowledge must provide some information rendering it technically plausible that the described compound or method has the claimed effect. This generally requires at least some experimental data demonstrating the effect.

The case relates to European patent 2 419 741, which had been maintained in amended form after opposition proceedings. The patent in maintained form related to a method of identifying subjects having an increased risk of mortality after receiving an antibiotic, by measuring the level of a protein called procalcitonin in a sample from the subject. In claim 1, the subject was defined as someone suffering from a primary non-infectious disease and not exhibiting any symptoms of a bacterial infection.

An appeal against maintenance of the patent was filed by the Opponent.

The case turned on a point of claim interpretation. What is meant by a "symptom of a bacterial infection?" The Board took the view that this meant any symptom that could be caused by a bacterial infection, whether or not it was actually the case in the subject in question.

This was particularly problematic for the Patentee Respondent because, in the Examples provided in the patent, the patients were suffering from acute heart failure with reported shortness of breath (which may be a symptom of heart disease). However, the Board considered "shortness of breath" to be a symptom of a bacterial infection, for example in pneumonia which can be bacterial in origin. On this interpretation it followed that the Examples provided in the patent did not fall within the scope of claim 1.

Without the support of the data provided in the Examples, the Board held that it would not be credible to the skilled person that the claimed diagnostic effect is achieved in the claimed patient group (i.e. those not exhibiting any symptom of bacterial infection). Furthermore, post-published evidence cannot be used to remedy the deficiency in accordance with Enlarged Board Decision G2/21. (In the present proceedings, the patients in the trial in the post-published evidence submitted also suffered from shortness of breath so the data would not have helped in any event.)

As a consequence, the patent as maintained was found to lack sufficiency.

This Decision underlines the importance of ensuring that evidence that a therapeutic or diagnostic effect is achieved is provided in an application as filed, and that the claimed patient group is correctly defined. Nevertheless, this author has some sympathy for the Patentee as it is somewhat unexpected that a claim be interpreted so as to exclude all of the disclosed Examples when a reasonable interpretation that would include them is available. It will be interesting to see whether the eventual Decision in G1/24 will follow the Enlarged Board's preliminary view that the description can be referred to in the course of claim interpretation, and one wonders whether this could have made a difference in the present case.