Our services are centred around intellectual property that can be registered. We protect innovation, design, and branding across all sectors of industry, and at all stages in the supply chain.

For each IP right we offer services covering strategic advice, pre-registration searches, registrations and renewals, oppositions and dispute resolution. We handle work throughout the world, working with local colleagues in over 100 countries.


Our attorneys specialise in one or more sectors of industry, which enables them to provide quality advice with a commercial focus.

Our patent specialists have detailed understanding of the background technology, which ensures that your patent applications are prepared with the correct scope, reducing the likelihood of challenges from third parties and objections from the patent office.

They also advise whether other forms of protection would be more appropriate. Our brand specialists work with brand managers for leading brands and their advice is commercially focussed making sure that you get the best value from your budget.

Where’s your supporting data? Plausibility at the EPO


In his article earlier this year, Zack Mummery discussed the role of plausibility in UK patent decisions. In this article, I will consider plausibility from an EPO standpoint and summarise the possible implications for your patent strategy.

Plausibility is a concept that frequently arises during European prosecution in the context of both sufficiency and inventive step, and particularly for patents and patent applications in the life sciences sector. It has implications for the amount of supporting data to include in a patent application and so is of great importance in devising a patent strategy: file early with fewer data and risk the patent application being found to lack sufficiency or inventive step through lack of plausibility; or delay filing and risk exposing the patent application to more prior art, or risk competitors beating you to the punch.

I briefly consider the EPO case law on this matter which appears to suggest that, in certain circumstances, a lack of data may not be as detrimental as one may expect.


One of the most commonly-cited EPO Board of Appeal decisions concerning plausibility is T1329/04. This case was directed to a polynucleotide encoding a polypeptide having GDF-9 activity. In relation to the closest prior art, the problem to be solved was defined as isolating a further member of the TGF-β superfamily. The Board investigated whether or not the problem had been plausibly solved, i.e. whether or not it is plausible that GDF-9 constituted a further member of the TGF-β superfamily.

However, the Board concluded that as a significant structural feature in TGF-9 differed from the members of the TGF-β superfamily, and no functional characterisation of TGF-9 was forthcoming in the application, the application did not sufficiently identify this factor as a member of this family. In other words, there was not enough evidence in the application to make it at least plausible that a solution was found to the problem which was purportedly solved.

The appellant filed post-published evidence (i.e. evidence published after the filing date) establishing that GDF-9 was indeed a growth differentiation factor. The Board held that this cannot be regarded as supportive of any evidence in the application as filed, since there was not any. In the Board’s view, even if supplementary post-published evidence may in the proper circumstances also be taken into consideration, the Board concluded that it may not serve as the sole basis to establish that the application solves indeed the problem it purports to solve. So, the Board held that there was no inventive step.

However, since T1329/04, there have been a number of important clarifications on the requirements for establishing plausibility.

Burden of proof and substantiating doubt

T578/06 concerned a patent application directed to the use of somatostatin or a somatostatin agonist in the formulation of a pharmaceutical formulation or preparation for the treatment of a human patient in receipt of transplanted isolated pancreatic islet cells.

The examining division had reasoned that the formulated technical problem had not been shown to be solved by the claimed invention and, consequently, that the requirements of Article 56 EPC were not met. It was argued in essence that the application as filed did not comprise experimental data showing the claimed effect.

The Board disagreed with the examining division and noted:

…the EPC requires no experimental proof for patentability and considers that the disclosure of experimental data or results in the application as filed and/or post-published evidence is not always required to establish that the claimed subject-matter solves the objective technical problem. This is in particular true in the absence of any formulated substantiated doubt as is the case here.

…the establishment of plausibility [is] is only relevant when examining inventive step if the case at hand allows the substantiation of doubts about the suitability of the claimed invention to solve the technical problem addressed and when it is thus far from straightforward that the claimed invention solves the formulated problem.

The Board then provided some examples of previous Board of Appeal decisions in which a substantiation of doubt had been established, one of which was T1329/04. The other decision referred to was T893/02, which concerned a patent directed to gp75 as a tumour vaccine for melanoma, in which the technical effect of inducing immunoprotection against melanoma would “probably not be expected” by the skilled person since the prior art taught that gp75 was not a protein present at the surface of melanoma cells and that anti-gp75 auto-antibodies are only very rarely found in the sera of melanoma patients. Thus, based on the mechanism of action involved, it was unlikely that the claimed composition would achieve the technical effect.

So, an important finding from T578/06 appears to be that the burden of proof is on the EPO to substantiate doubt that the technical problem is solved, but that doubt may be established by, for example, a structural (T1329/04) or mechanistic (T893/02) teaching-away in the prior art.

In T578/06, the Board decided that it had no reason to doubt the usefulness of somatostatin for the alleged effect, and that under these circumstances, post-published evidence may be taken into account. An inventive step was acknowledged.

Plausibility threshold and the squeeze between plausibility and inventive step

Problems may arise if plausibility is called into question and the application as filed lacks data demonstrating that a technical effect is plausibly solved. In this situation, applicants may find themselves in a squeeze: rely on prior art or common general knowledge to demonstrate plausibility at the filing date, and the EPO finds a lack of inventive step based on that same prior art or common general knowledge; or if there is no prior art or common general knowledge to demonstrate plausibility, the technical effect may not be considered to be plausibly solved.

However, case law suggests that it may be possible to avoid such a squeeze, even if the application as filed lacks supporting data.

T108/09 concerned a patent directed to the use of fulvestrant as a third line breast cancer treatment in patients who had previously been treated with an aromatase inhibitor and tamoxifen and had failed such previous treatments. The patent contained a protocol for a clinical trial but not its results. The patentee did, however, provide post-published results of the clinical trial which demonstrated that that the problem had, indeed, been solved. The opponent argued that it was not plausible that the technical problem was solved.

In T108/09, the Board differentiated the case from T1329/04 and indicated the following:

In the present case, however, it was already known that fulvestrant was effective as a second-line agent in the treatment of breast cancer…. Regarding the use of fulvestrant as a third-line agent, which constitutes the contribution of the present invention to the state of the art, the patent in suit contains, as was mentioned above… detailed information as to how fulvestrant has to be formulated and administered in order to obtain the desired effect. [The post-published evidence] is therefore far from being the only source of information regarding the question whether fulvestrant is useful as a third-line agent, so that the data contained therein may be used in the evaluation of whether or not the problem underlying the present invention has been plausibly solved.

During the Appeal proceedings, the patentee had argued that although prior art had indicated that fulvestrant could be used as a second line treatment against tamoxifen-resistant tumours, this knowledge alone was not sufficient to assume that fulvestrant would be successful as a third-line treatment against tumours that proved to be resistant to tamoxifen and aromatase inhibitors. The patentee argued that due to lack of any indication that fulvestrant may be successful as a third-line treatment, there was no reasonable expectation of success.

The Appeal Board held that the patent was inventive.

This decision appears to suggest that plausibility is a ‘threshold’ test and that if one relies on prior art or common general knowledge of evidence of plausibility (in this case that fulvestrant was effective as a second line breast cancer treatment), it does not necessarily follow that the invention is obvious (i.e. that there is no reasonable expectation of success that it may work as a third line breast cancer treatment). Similarly, even if a problem is plausibly solved, it does not necessarily follow that it is inventive. In other words, plausibility and obviousness are not two sides of the same coin.

A threshold for plausibility has also been discussed in the English courts. Justice Carr in a UK High Court Decision (Actavis UK Limited v. Eli Lilly and Company EWHC 3294 (Pat) (High Court 2015) (Carr, J.)), articulated the following:

[f]or obviousness, a fair expectation of success is required because, in an empirical art, many routes may be obvious to try, without any real idea of whether they will work. The denial of patent protection based upon the “obvious to try” criterion alone would provide insufficient incentive for research and development in, for example, pharmaceuticals and biotechnology, and would lead to the conclusion that a research program of uncertain outcome would deprive a patent of inventive step. The reason why the court requires that the invention of a patent should be plausible is different. It is to exclude speculative patents, based on mere assertion where there is no real reason to suppose that the assertion is true.

Plausibility for sufficiency or inventive step?

The EPO Guidelines for Examination (F-III, 12) illustrate the relationship between inventive step and sufficiency. They state that if the claimed invention lacks reproducibility, this may become relevant under the requirements of sufficiency of disclosure or inventive step. If an invention lacks reproducibility because its desired technical effect as expressed in the claim is not achieved, this results in a lack of sufficient disclosure, which has to be objected to under Art. 83 (i.e. sufficiency). Since the technical effect is part of the solution proposed in the claim, it cannot be part of the problem underlying the application. Otherwise, i.e. if the effect is not expressed in the claim but is part of the problem to be solved, there is a problem of inventive step.

Consequently, if the claim is a second medical use claim in which the technical effect (i.e. the new medical use) is defined in the claim, if doubts are raised as to the plausibility of achieving the new medical use, then an objection is likely to be raised under sufficiency. Nevertheless, the concepts surrounding assessment of plausibility should apply equally to its discussion under sufficiency and inventive step.

In T609/02, the Board of Appeal held that the specification must disclose the suitability of the agent for the claimed therapeutic application, but that absolute proof of efficacy, or clinical trials, was not necessary. A mere assertion, however, was not enough. In vivo tests are not necessary and in vitro tests could suffice if the skilled person would know from the prior art, or the specification, that the in vitro effect shown has a direct bearing on the disease in question. It was emphasised that post-filed evidence could only be used to back up the findings provided in the patent application, and not in itself to establish sufficiency of disclosure.

Implications for patent strategy

It is always preferable to include as much data as possible to demonstrate the technical effect of an invention over the scope of the claim, or to indicate a medical use over the scope of the claim.

If you have an invention but you may not have much supporting data (at least yet), it is usually advisable to file an initial patent application rather than wait until more data is available. Filing an initial patent application would begin a 12 month period (the ‘priority year’) in which further applications may be filed which can include updates, such as additional data, as and when they become available. The subsequent patent applications filed within the priority year may then claim priority back to the initial patent application in respect of subject-matter supported by the initial patent application. If there is still a lack of data at the end of the priority year (when a decision is typically made on whether to pursue foreign patent protection) there may be the option of withdrawing the patent application and refiling it to begin the priority year once more. If, however, it is not clear whether enough data is available at the end of the priority year, very careful consideration is required to decide whether to proceed with the application (to preserve the original priority date but risk a finding of lack of plausibility), or whether to withdraw the patent application (losing the priority date and risking exposure to more prior art, but preserving the option of including further data in a new filing to reduce the risk of a plausibility challenge).

Points to consider

  • If an EPO Examiner raises a lack of inventive step or sufficiency by citing a lack of plausibility, it is important to check that they have met their burden of substantiating doubt. If not, then there may an argument of prima facie plausibility.
  • If you wish to challenge a third party patent for lack of plausibility, you may substantiate doubt by, for example, demonstrating that there is a mechanistic or structural teaching away in the prior art or common general knowledge which would give reason to expect that the problem is not plausibly solved or that a medical use is not plausibly achieved.
  • If plausibility is called into question, in some circumstances it may be possible to establish plausibility by reference to prior art or common general knowledge. Reference to prior art or common general knowledge in support of plausibility may not necessarily lead to a finding of lack of inventive step. This is because plausibility appears to be a threshold test which is not assessed in the same way as whether an invention is obvious to try with a reasonable expectation of success.

This article is for general information only. Its content is not a statement of the law on any subject and does not constitute advice. Please contact Reddie & Grose LLP for advice before taking any action in reliance on it.

Saved Staff
Staff member

Remove all

Call +44 (0)20 7242 0901
Call +44 (0)1223 360 350
Call +49 (0) 89 206054 267
Call +(00) 31 70 800 2162
This field is for validation purposes and should be left unchanged.