UK divergence from the EPO on plausibility (Sandoz v BMS), Part 1: Is the "plausibility" test the same for both sufficiency and inventive step?

This Kat took the enforced confinement of a rainy summer weekend to finally delve deeper into one of the key patent decisions from the UK courts this year. The Court of Appeal decision in Sandoz v BMS ([2023] EWCA Civ 472) attempted to reconcile the EPO and UK approaches to plausibility. There is a lot to unpack in Sandoz v BMS and the following is Part 1 of 2. Part 1 will look at divergence between the EPO and UK on the legal test for sufficiency. Part 2 will consider the Court of Appeal's interpretation of G 2/21. 

The Court of Appeal in Sandoz v BMS attempts to reconcile the Enlarged Board of Appeal (EBA) decision in G 2/21, and the landmark UK Supreme Court decision on plausibility Warner-Lambert v Actavis [2018] UKSC 56. However, to this Kat, the Court of Appeal is not entirely successful. Unlike the EPO, Lord Justice Arnold (Arnold LJ) in Sandoz v BMS considers the "plausibility" of a non-claimed technical effect under the heading of inventive step and sufficiency. In doing so, the Court of Appeal departs from the EPO on the appropriate legal test for sufficiency. To this Kat, this departure ultimately leads to a misinterpretation of G 2/21 by the Court of Appeal, given that G 2/21 relates specifically to the standard of evidence test for inventive step, not sufficiency. 

Sandoz v BMS: Facts of the case

The case in Sandoz v BMS related to BMS's European (UK) patent EP 1427415. Claim 1 of the patent was a product claim for a compound, apixaban, defined by its chemical formula. Apixaban is a factor Xa inhibitor, marketed by BMS in Europe as a treatment of thromboembolic disorders. Sandoz and Teva brought a revocation action against the patent on the grounds of insufficiency and inventive step. Particularly, Sandoz and Teva argued that the ability of apixaban to inhibit factor Xa was not "plausible" in view of the application as filed. 

The question before the Court of Appeal in Sandoz v BMS was similar to that considered in G 2/21. Particularly, how much evidence is needed to support a purported (non-claimed) technical effect of an invention relied on for inventive step?

The application as filed of the disputed patent described a large number of compounds, including apixaban, and included some generic statements that these compounds could be used as inhibitors of factor Xa. The technical effect relied on for inventive step of a claim to apixaban per se was the efficacy of apixaban as a factor Xa inhibitor. However, the application as filed did not provide data specifically showing that apixaban was a factor Xa inhibitor. 

Did the Court of Appeal fall down
the plausibility rabbit hole?

The High Court ([2022] EWHC 822 (Pat)) found the patent to lack sufficiency and inventive step. Particularly, the judge found that it would not have been plausible to a skilled person at the filing date that apixaban was a factor Xa inhibitor. BMS appealed the decision to the Court of Appeal on the grounds that the law on plausibility had been misapplied. 

Plausibility in inventive step versus sufficiency at the EPO

Plausibility often causes confusion because it is a term employed in both sufficiency and inventive step analysis. However, the EPO's use of the term plausibility in both of these contexts makes sense if we remember that plausibility is merely a catch-word that the EPO uses to signal a higher level of underlying doubt with respect to certain types of invention (sufficiency) or the purported technical effects of certain types of invention (inventive step) (see also IPKat: Plausibility demystified - a review of EPO case law before G 2/21). 

In order to be sufficiently disclosed under Article 83 EPC, a detailed description of at least one way of carrying out the invention must be given in the application. An objection of insufficiency requires there to be serious doubts, substantiated by verifiable facts, that the skilled person would be able to work the invention (II-C, 9). The sufficiency bar can usually be satisfied by providing a single example falling in the scope of the claim in the application as filed.  

At the EPO, if a functional effect of an invention is explicitly specified in a claim (e.g. "wherein the drug treats the disease"), the evidence for the invention is considered under the heading of sufficiency (Article 83 EPC). For some types of claimed inventions, such as therapeutic inventions, there is a higher level of underlying doubt that a skilled person would be able to work the invention over the full scope of the claim. The plausibility test in sufficiency is the way in which the EPO signals the higher level of underlying doubt with respect to these types of invention. 

If the functional or technical effect of an invention is not expressed in a claim, but contributes to the problem the invention purports to solve (e.g. the functional properties of a new chemical compound), the evidence for the effect is considered under the heading of inventive step (Article 56 EPC). In other words, the question becomes whether there is enough evidence to convince a skilled person that the invention does actually solve the problem it purports to solve in view of the closet prior art (T 0939/92, G 1/03). For some types of invention, there may be more underlying doubt that the technical effect is actually achieved. The plausibility test in inventive step is the way in which the EPO signals this higher level of underlying doubt with respect to the effect of certain types of invention. 

At the EPO, it is therefore rare for a product claim lacking broad functional language to be invalidated for lack of sufficiency (or plausible sufficiency). The test for sufficiency is merely whether a skilled person would be able to perform the claimed invention over the full scope of the claim, which is very narrow if the claim is to a single compound. If the claim is to a drug, a skilled person is able to perform the invention if they are able to make the drug. At the EPO, as confirmed in G 2/21, the evidence for a non-claimed technical effect only becomes relevant with respect to inventive step and is not relevant for sufficiency (EPO Guidelines for Examination, F-III-12; G 1/03, r. 2.5.2; G 2/21, r. 77). However, the UK Court of Appeal in Sandoz v BMS did not make the same distinction with respect to the evidence for a technical effect in inventive step and the evidence for sufficiency.  

Plausibility in inventive step and sufficiency in the UK

Eliquis

The High Court in Sandoz v BMS did not follow the same schema for the application of the "plausibility test" as the EPO. Particularly, the High Court chose to consider "plausibility" as an umbrella term spanning both sufficiency and obviousness, almost as if it were a legal test in-and-of-itself (para. 153-233). Arnold LJ in the appeal case ([2023] EWCA Civ 472) also did not make a clear distinction between plausibility for sufficiency and plausibility for inventive step. On the contrary, Arnold LJ accepted that if the claim lacked plausibility for a technical effect relied on for inventive step, it necessarily also lacked plausibility for sufficiency (para. 4). To this Kat, the UK approach does not appear aligned with the EPO case law (G 1/03, r. 2.5.2). But does the UK tendency to consider the plausibility of a technical effect under the headings of both sufficiency and inventive step, have any practical consequences? 

Inventive step or sufficiency, why does it matter?

In Sandoz v BMS it was "common ground" that it made "no difference to the outcome whether the issue is viewed as one of inventive step or one of sufficiency" (para. 4). However, the EBA referral on "plausibility" considered by Arnold LJ in Sandoz v BMS, related very particularly to inventive step analysis, not sufficiency.  Furthermore, the reasons behind the referral in G 2/21 particularly stemmed from consequences of the EPO's problem-solution approach to inventive step analysis. Does it therefore make sense to apply G 2/21 in the context of sufficiency?

The applicability of G 2/21 to UK case law is complicated by the fact that the issues leading to the referral in G 2/21 are arguably not as relevant in the UK as they are at the EPO. The UK uses the Windsurfer/Pozzoli test for inventive step instead of the EPO's preferred problem-solution approach. In contrast to Windsurfer/Pozzoli, the problem-solution approach requires the "closest prior art" to be identified. However, the exact document representing the "closest prior art" may not be known to an applicant at the filing date. If a patentee was unaware of obscure prior art at the filing date, they will not have had the opportunity to ensure the application contained sufficient data demonstrating the superiority of the invention over this prior art should it later be cited as the "closet". The patentee may also face the related problem of new data submitted by an opponent purporting to disprove the originally proposed technical effect relied on for inventive step. This was, of course, exactly the situation in G 2/21.

A patentee can therefore very easily fail to explicitly mention or provide data for the particular technical effect of an invention on which they must later rely. In the field of antibodies, this may amount to the mere admission in the application as filed of the exact test by which the affinity of a new antibody was measured. 

The decision of the EBA in G 2/21 primarily related to the question of the standard of evidence required to support a purported technical effect relied on for inventive step. Central to the reason for the referral was the fact that the purported technical effect was not claimed, but proposed post hoc by the patentee in response to data submitted by an opponent allegedly disproving the original purported technical effect. The question at the heart of G 2/21, namely whether post-filed evidence could be used to support a technical effect relied on for inventive step, was thus very different to the question of whether a skilled person would be able to work the invention. As confirmed by the EBA in G 2/21, "the scope of reliance on post published evidence is much narrower under sufficiency of disclosure (Article 83 EPC) compared to the situation under inventive step (Article 56 EPC)" (r. 77). However, the test for sufficiency is generally easier to meet than the evidence bar for inventive step. The Court of Appeal, in considering the case in question in view of G 2/21, did not take account of these critical distinctions. 

Application of EPO case law on plausibility in Sandoz v BMS

A full understanding of why G 2/21 specifically relates to inventive step as opposed to sufficiency, reveals the difficulty of applying the order to G 2/21 in the context of UK "plausibility" case law. In Sandoz v BMS it was uncontentious that the claimed product, apixaban, did have the technical effect relied on for inventive step. The appropriate question in view of G 2/21 would have been whether this technical effect was "encompassed and embodied" by the application as filed. The question under the normal EPO approach would not have been to consider the plausibility of the technical effect under the heading of sufficiency. However, the High Court and Court of Appeal did not consider there to be any distinction between plausibility for inventive step and plausibility for sufficiency.

In their appeal, BMS submitted that the High Court "erred in law because, in the case of a claim to a single chemical compound, there is no requirement that the specification makes it plausible that the compound is useful. It is sufficient that the specification discloses the structure of the compound and a method of synthesis and contains an assertion of potential utility for the compound, provided that that assertion is not manifestly speculative or wrong." (para. 89). However, Arnold LJ dismissed this ground of appeal, citing T 488/16 (BMS/Dasatinib) in which the Board of Appeal found that post-filed evidence could not be used to rescue a narrow product claim. Crucially, however, T 488/16 related to inventive step and the problem of post-filed evidence to support a post-hoc inventive step argument based on newly cited prior art. T 488/16 did not relate to sufficiency. 

Final thoughts (Part 1)

At the heart of the divergence between the UK and EPO on the test for the standard of evidence for a patent, is the way in which the UK courts continue to treat plausibility almost as if it were a legal standard specified by the patent act. In G 2/21, the EBA dismissed "plausibility" as a generic catch-word that does not amount to a distinctive legal concept. By contrast, in Sandoz v BMS, Arnold LJ was reluctant to move away from the language of "plausibility" as an umbrella term spanning both sufficiency and inventive step. 

The High Court and the Court of Appeal in Sandoz v BMS have thus further muddied the waters between sufficiency and inventive step by grouping both under the catch-phrase "plausibility". In this Kat's view, in doing so, the UK case law is at risk of departing from the EPO on the law of sufficiency. Furthermore, the UK tendency to take a blanket approach to the application of plausibility case law to both inventive step and sufficiency, also ignores the whole raison d'etre behind the referral in G 2/21, and ultimately leads to potential misapplication of the G 2/21 by the Court of Appeal. For full analysis, see Part 2. 

EPO

• Plausibility demystified - a review of EPO case law before G 2/21 (Feb 2023)
• G 2/21: Is the technical effect embodied by the invention as originally disclosed? (March 2023)
• To encompass and embody: Applying the abstract principles of G 2/21 (March 2023)
• Applying G 2/21: Preliminary opinion from the referring Board of Appeal on post-filed evidence appeal (T 0116/18) (June 2023)

UK courts

• No pain, no gain: Plausibility in Warner-Lambert v Actavis (2018)
• Takeda v Roche: "Is it plausible? Is it true?" (Aug 2019)

US (Enablement & Written Description)

• Patenting Antibodies: The epitope claim is dead, long live the epitope claim (Nov 2021)
• Strict US written description requirement applied to CAR-T-cell therapy (Juno v Kite) (Jan 2022)
• US Supreme Court decision in Amgen v Sanofi: The European Perspective