September 2026 In this recent EPO Board of Appeal (BoA) decision, the claims of European patent No. 3288980 were found to lack basis in the application as filed as a result of the BoA’s reluctance to accept a bespoke meaning of the term “monotherapy” advanced by the patentee. The decision serves as a useful reminder that non-standard definitions must be clear, consistent and reflected in the claim language itself, particularly as questions around claim interpretation and added matter remain under close scrutiny while we await the outcome of G 1/26.
Background
The case concerned Bristol-Myers Squibb’s (BMS) European patent No. 3288980, which was directed to the treatment of PD-L1-positive melanoma by administering nivolumab as a monotherapy.
The patent had previously been revoked by the Opposition Division for added matter. BMS appealed this decision and, on appeal, the key issue was how the term “monotherapy” in the granted claim should be interpreted, because the question of whether the claim added matter rested largely on the interpretation of this term.
BMS argued that, in light of the description, the term “monotherapy” should not be limited to treatment with nivolumab alone but, instead, should be understood as excluding only combination therapies involving an anti-CTLA-4 antibody, while still permitting combinations with other active agents.
Commercially, it was important to BMS that this interpretation prevailed because BMS markets nivolumab both as a standalone treatment and in combination with another active agent, relatlimab. The Board’s acceptance of the broader interpretation of “monotherapy” would therefore have meant that the claims of EP 3288980 covered BMS’ commercially important combination therapy, as well as nivolumab as a standalone treatment.
Before considering BMS’ argument, the Board began by confirming a familiar but important principle: before added matter can be assessed, the claim must first be construed. Accordingly, the Board noted that only once the meaning of the claim has been established can the “gold standard” for added matter be applied.
Construction
The Enlarged Board of Appeal decision G 1/24 provides a clear teaching that the description and drawings must always be consulted when interpreting the claims, not only in cases where the claims are unclear.
What G 1/24 does not fully resolve, however, is what the step of “consulting” the description actually requires in every context. In particular, there remains uncertainty over whether an unconventional definition in the description can override an ordinary meaning of an otherwise clear term in the claim, especially when that interpretation affects added matter.
Whilst the more recent Enlarged Board decision G 1/25 confirms that the claims are not to be interpreted in isolation and that definitions provided in the description for terms used in the claims are to be taken into account, provided they are “technically reasonable” and consistent with the overall teaching of the specification as a whole, it does not go as far as addressing the relationship between claim interpretation and added matter.
This unresolved issue is now part of a broader debate before the Enlarged Board in G 1/26, which asks how far the description and drawings can influence claim interpretation when assessing compliance with Article 123(2) EPC.
In the present BoA decision, claim 1 of the main request was directed to a composition comprising nivolumab for use in treating melanoma in a PD-L1-positive patient. The treatment was to involve a flat dose of 480 mg nivolumab once every four weeks, administered “as a monotherapy”. The claim also included a negative feature stating that nivolumab was not administered in combination with an anti-CTLA-4 antibody.
BMS relied on the negative feature in the granted claim, together with an unconventional definition in the description, to argue that the term “monotherapy” in the granted claim should not be interpreted, as it typically would be, to refer to a single drug, but should instead be interpreted to exclude only combinations involving anti-CTLA-4 antibodies, while permitting other combination therapies.
Both sides accepted that the ordinary meaning of “monotherapy” is treatment with a single drug, and the Board saw no sufficient reason to depart from that conventional meaning.
BMS pointed to a passage in the granted description stating that “anti-PD-1 antibody monotherapy” includes therapy with an anti-PD-1 antibody without anti-CTLA-4 antibody therapy. In BMS’ view, this definition, in combination with the negative feature recited in the granted claim, was sufficient to support the argument that the term “monotherapy” in the granted claim should cover combination therapies, provided that those combination therapies did not involve anti-CTLA-4 antibodies.
The Board disagreed and found that the negative feature in the granted claim, together with the definition of “anti-PD-1 antibody monotherapy” in the description, was not sufficient to support the patentee’s modified definition of the term “monotherapy”. Instead, against the widely understood conventional meaning of the term “monotherapy”, the negative feature in the granted claim and the bespoke definition of “anti-PD-1 antibody monotherapy” in the description merely introduced ambiguity.
The Board also drew a clear distinction between the phrase “anti-PD-1 antibody monotherapy” defined in the description and the broader standalone term “monotherapy” used in the granted claim. Due to this distinction, the Board was not prepared to import the unconventional definition from the description into the claim.
Accordingly, the Board held that the term “monotherapy” retained its usual meaning and that the granted claims were, therefore, limited to methods of treatment involving administration of nivolumab as a single drug.
Added Matter
Once it had been agreed that the term “monotherapy” should be construed in its ordinary sense, the Board turned to the application as filed and the relevant question became whether the original disclosure directly and unambiguously disclosed nivolumab, at the claimed flat dosage of 480 mg once every four weeks, as a true single-drug therapy for the treatment of PD-L1-positive melanoma.
The opponents argued that the original disclosure did not directly and unambiguously disclose the specific combination of nivolumab as a true single-drug therapy with the claimed flat dosage. In support of their argument, the opponents noted that the application as filed did not refer specifically to administration of nivolumab in the required flat dosage but, instead, referred more generally to administration of an anti-PD-1 antibody in that flat dosage.
The opponents also pointed out that the application as filed did not use the term “monotherapy” but instead used the expression “anti-PD-1 antibody monotherapy”. Further, in the application as filed, the expression “anti-PD-1 antibody monotherapy” was used in quotation marks and parentheses, suggesting that, in the context of the application as filed, this term should be interpreted as having a special definition, rather than its ordinary meaning.
The Board accepted the opponents’ arguments and agreed that, in the context of the application as filed, the expression “anti-PD-1 antibody monotherapy” had been used to refer to therapy with an anti-PD-1 antibody but without anti-CTLA-4 antibody therapy. Thus, unlike the term “monotherapy” in the granted claims, the term “anti-PD-1 antibody monotherapy” in the application as filed was interpreted by the Board as covering combination therapies, provided that the combination therapy did not involve an anti-CTLA-4 antibody.
Crucially, this interpretation was not considered to influence the Board’s earlier interpretation of the standalone term “monotherapy” in the granted claim.
The Board then contrasted its interpretation of the expression “anti-PD-1 antibody monotherapy” in the application as filed with its earlier interpretation of the standalone term “monotherapy” in the granted claim and found that, as a result of the contrasting interpretations, the granted claim recited a combination of features that was not directly and unambiguously disclosed in the original application.
Accordingly, the main request was found to add matter, after which the appeal was dismissed and the patent remained revoked.
Discussion
The patentee’s unsuccessful attempt to rely on a modified definition of a well-known term of art in the description of the granted patent to overcome the prior art without excluding a commercially relevant embodiment of the invention serves as a reminder that bespoke definitions, although useful in some scenarios, can be dangerous, particularly if they are not used consistently.
Importantly, where drafters intend to rely on a bespoke definition of a term, that definition should be used clearly and consistently throughout, from the application as filed through to the granted claims and description. In some cases, best practice may be to have that bespoke definition in the claims. By ensuring that the same wording is used consistently throughout the drafting and prosecution process, patentees and attorneys reduce the risk of situations like this one, where a term used in the granted claim is interpreted differently from the corresponding term in the application as filed, leading to irresolvable added matter issues downstream.
Although this decision does not fully address the questions put to the Enlarged Board in the referral of G 1/26, it comes at an opportune time to highlight the pressing need for those questions to be answered as we await the Enlarged Board’s response to the referral.
