File-wrapper estoppel (also call “prosecution history estoppel”) is a term used to indicate that an applicant of a patent application that has made “narrowing amendments” to the claims of the patent application, for example to take into account prior art, may be precluded from broadening the scope of their granted claims to cover subject-matter which has been given up by the narrowing amendments. The term is well-known in the United States, where courts have regularly looked at the prosecution history when interpreting patent claims. However, in some European countries, the concept is also known, and the question will soon arise whether judges in the European Unified Patent Court will also consider the prosecution history when interpreting the claims of a patent.
In a recent article, published in GRUR Patent, 2023, 34 (available through a paywall at this link), the authors reviewed the legal situation in a number of European countries. Some countries, such as Germany, have traditionally not acknowledged the concept of file-wrapper estoppel. However, the Federal Supreme Court has in one instance barred a plaintiff from alleging infringement of a product under the Roman law doctrine of “venire contra factum proprium” (i.e., prohibition of inconsistent behaviour). A similar principle exists in France, whereas in the Netherlands statements made by the patent owner may be used by a third party to the disadvantage of the patent owner.
This inconsistent practice in Europe leads to the question – how will Europe’s new Unified Patent Court deal with this challenge? The authors of the GRUR article argue strongly in favour of introducing the concept into the UPC’s jurisprudence. They argue that the file wrapper is an important source of information as it can show what exactly the patent owner wanted to protect and for what and why they actually obtained this protection. This, the authors argue, is also consistent with the principle that the patent owner should only get protection for what they actually disclosed.
Even if the recent decision T 169/20 of the European Patent Office’s Boards of Appeal in an opposition case highlighted that the claims should be read by themselves and that the support of the description for interpreting the claims should only be resorted to in exceptional cases in which the subject-matter of the invention and/or its technical context needs to be clarified, this does not exclude at least referring to the file-wrapper to better understand the scope of the claims. It is true, as the T 169/20 decision clarified, the support of the description should, in any case, not be used for restricting or modifying the subject matter of the invention beyond what a person skilled in the art would understand when reading the wording of the claims within the relevant technical context. This was, however, an opposition case in which the assessment of the relevance of prior art was carried out. In infringement cases, there are likely to be, in practice, cases in which it would not be justified to conclude that a product or service infringed the claims of a granted patent based on the statements made during the prosecution of the file.
At Sonnenberg Harrison Partnership, we regularly review the prosecution history file when assessing or defending an alleged infringement. We know that it is many European courts have traditionally not taken, but it is often true that additional arguments can be found to defend or assert the patent from the documents.
