Case Nos: CA-2024-002655/002675/002676 - [2025] EWCA Civ 936

The appeal

The Claimants’ starting point is that (i) the judge was correct to note at [278] that no challenge was made to the technical reasoning which Prof Westwell put forward in support of obviousness over the Poster and (ii) each of the three reasons for non-obviousness advanced by Astellas, based on the evidence of Prof Ward, was rejected by the judge. In those circumstances, the Claimants submit, the irresistible conclusion is that the invention claimed in the Patent was obvious in the light of the Poster.

The Claimants contend that, in reaching the opposite conclusion, the judge erred in principle in two ways. First, they argue that the judge erred in looking for a “context” or “scenario” for what was technically obvious. The skilled person or team is deemed to be interested in alternative ways of achieving essentially the same result as that obtained by the prior art and this, of itself, provided sufficient context.

Secondly, the Claimants argue that the judgment contains an internal inconsistency in that the judge rejected an allegation that Prof Westwell’s cross-examination showed that he had approached the question of obviousness over the Poster with hindsight at [287 (iii)] and [288], but later in the judgment at [338(i)-(v)] he held in relation to the same cross-examination that Pozzoli step 3 was leading and that Prof Westwell’s conclusion was tainted with hindsight.

So far as the first argument is concerned, the Claimants emphasise that, as discussed above, motivation to take a particular step is not a necessary condition for a finding of obviousness. It is possible for a patent to be found obvious because a step is technically obvious even if the skilled person has no motive to take it because the existing solution produces a perfectly acceptable result: see, for example, Research in Motion UK Ltd v Visto Corp [2008] EWHC 335 (Pat), where Floyd J stated at [73] that the court “will readily assume that technicians and businessmen will wish to make trivial changes to what is known in order to produce essentially the same result.”

As I read the judgment, the judge did not question this. The point he made in [338](iii) is that whether a change is properly characterised as “trivial” is highly fact-dependent, and there is a real danger that the question of “triviality” is substituted for that of obviousness. In general, he agreed with Astellas that the issue of “triviality” is not well suited to the field of medicinal chemistry, but it all depended on the context. As he had explained at [198], the fact that a modification to a compound is “small” in structural terms does not necessarily mean that it will obviously have no material effect.

Nor do I understand the judge to have questioned the legitimacy of approaching the issue of obviousness on the footing that the skilled team, having read the Poster, would be interested in developing an antagonist for HS and HR prostate cancer that was simply an alternative to RD162.

The point that the judge made at [292] and [338](ii) was a different one: in assessing Prof Westwell’s evidence, it was significant that Prof Westwell had not said that he was approaching the issue on the premise that the skilled team, having read the Poster, would be interested in developing an antagonist for HSPC and HRPC that was simply an alternative to RD162. Indeed, Prof Westwell did not explain what objective the medicinal chemist would have in mind at all. This is what the judge meant by the absence of “context” or “scenario”.

Counsel for the Claimants’ first response to this was to point out that Prof Westwell had stated in 9.49 that the medicinal chemist “would expect certain variants of RD162 to have the same or similar activity and therefore also have therapeutic potential” and in 9.51 that it would be “immediately obvious … that the following two compounds would be likely to have therapeutic potential that was similar to that of RD162” (emphases added). Thus, he argued, Prof Westwell was considering what obvious alternatives to RD162 would be expected to have similar activity. The difficulty for the Claimants is that these paragraphs form part of Prof Westwell’s reasoning for the conclusion he expressed in 9.47. They are not a substitute for an articulation by Prof Westwell of the premise upon which he considered the question of obviousness. The judge was entitled to take that omission into account when assessing Prof Westwell’s evidence.

As counsel for Astellas submitted, if Prof Westwell had approached the issue in that way, one would have expected him to consider (among other things) the question identified by the judge in the context of the “take forward RD7” case at [308]: starting from RD162, why would the medicinal chemist go back from a cyclobutyl group to geminal dimethyl groups at position X when comparison between RD7 and RD37 indicates that RD37 (with a cyclobutyl group) is more active than RD7 (with geminal dimethyl groups)? At the very least, one would expect this question to be discussed between the medicinal chemist and the cancer biologist, but Prof Westwell says nothing about any such discussion. He does not say, for example, that he has been informed by Prof Hickson that the cancer biologist would regard the activity of RD7 as acceptable even though it is less than that of RD37. Instead, Prof Westwell’s focus in 9.50 was upon the effect of changes at position X on PK-DM issues, which would be within the remit of the medicinal chemist.

Counsel for the Claimants argued that the judge was not entitled to make the finding he made in [311], [314] and [316] that RD37 had better activity than RD7, particularly in the HRPC PSA level assay, since it was based on an incorrect recollection of the evidence of Prof Hickson. This is not a ground of appeal for which the Claimants have permission. Furthermore, it is a challenge to a finding of fact as to how the results reported in the Poster would be interpreted by the skilled team, and therefore can only succeed if that finding was rationally insupportable. The judge considered the evidence of both Prof Clarke and Prof Hickson on this topic in [310], and he understood them to have been agreed. Thus the finding was not based solely on the evidence of Prof Hickson, and it was certainly not insupportable.

Counsel for the Claimants also argued that, even if the judge’s finding was correct, it was plain that the activity of RD7 was acceptable because the data in the Poster showed that it was materially better than bicalutamide, which was the standard of care. Indeed, as the judge noted at [169], “all the RD compounds show much improved antagonist profiles and more significant reduction of PSA levels”. For a skilled team seeking an alternative to RD162, the key criterion would be better activity than bicalutamide, and it would not matter if the alternative was (say) 15% less active than RD162 if it was materially better than bicalutamide. While I see the force of this argument, the fact remains that no such approach was articulated by Prof Westwell in his report.

Counsel for the Claimants’ second response to the point identified in paragraph 85 above was to argue that it was common ground between Prof Westwell and Prof Ward that the medicinal chemist would consider obvious alternatives to RD162 that they would expect from reading the Poster to retain the desired biological activity. For this purpose counsel for the Claimants relied upon certain passages in Prof Ward’s reports in which Prof Ward said, for example, that the Poster “gives the Skilled Chemist a portion of the compound (the RHS substitutions) that they can vary and seek to modify, while retaining a degree of confidence that the desired biological activity will be preserved”. Again, however, this argument misses the point, which is that this approach was not expressed by Prof Westwell in his first report.

Turning to the second error of principle which the Claimants contend that the judge made, I see no inconsistency in the judge’s reasoning. In [287](iii) and [288] the judge was addressing Astellas’ submission that the passage of cross-examination the judge quoted in [285] demonstrated that Prof Westwell’s reasoning was tainted with hindsight, in particular because he had had the target (RD162') clearly in mind. The judge did not accept that submission.

At [289]-[297] the judge considered a different submission by Astellas, namely that it was nevertheless clear from his reports that Prof Westwell’s approach was infected with hindsight. The judge did not give his answer to that submission in this passage, but he did note (i) the absence of context discussed above, (ii) the sequence in which Prof Westwell had considered the documents and (iii) the way in which Prof Westwell’s first report was structured.

The judge expressed his conclusion in [338](iv) and (v): Prof Westwell’s evidence was tainted with hindsight, because the skilled team looking for a novel compound (i.e. an alternative to RD162) would not have been motivated to consider close analogues of RD162. The focus on close analogues was driven by the hindsight knowledge that the Patent claims RD162'.

Counsel for the Claimants argued that this conclusion was predicated upon the judge’s finding in [338](ii) that “the invitation put to [Prof Westwell] was leading”, which was inconsistent with [288]. I disagree. As the judge said in [288], there is “a subtle difference between having the target [i.e. RD162'] clearly in mind and considering whether it was obvious to make a change at position X [of RD162] from the cyclobutyl group to a dimethyl group”. The judge was not persuaded that it was established that Prof Westwell had had the target clearly in mind. The judge went on in [338](ii) to find that Prof Westwell “was asked to consider the change from cyclobutyl to dimethyl and asked whether that change would have a material effect”, which was leading.

Counsel for the Claimants also argued that this criticism was unjustified for two further reasons. First, the cross-examination was about the Slides, not the Poster, and the judge stated at [379] that Prof Westwell’s approach to the Slides “was less clearly redolent of hindsight”. Secondly, Prof Westwell had been instructed by the Claimants to adopt the Pozzoli approach, which he had faithfully followed, and that could not be condemned as leading.

I do not accept these arguments. So far as the first point is concerned, counsel for Astellas submitted that the relevant part of the cross-examination concerned both the Slides and the Poster, but the passage which the judge quoted focussed on the Slides. That does not avail the Claimants because, as the judge noted at [286], Prof Westwell confirmed that he had adopted the same approach in relation to the Poster. Moreover, as the judge noted at [295], Prof Westwell formed his opinion in relation to the Slides before being asked to consider the Poster. Thus hindsight was inevitably more of an issue with respect to the Poster than with respect to the Slides. As the judge remarked, it is odd that Prof Westwell’s report was structured the other way round.

As for the second point, I do not understand the judge to have criticised the Claimants for instructing Prof Westwell to adopt the Pozzoli approach or Prof Westwell for doing his best to follow it. The judge’s concern was that Prof Westwell was nevertheless led to focus on changing cyclobutyl to dimethyl at position X (rather than making other modifications to RD162) and whether that would have a material effect, rather than considering what would be an obvious way forward from RD162. In other words, as with many quizzes, there was a clue to the answer in the phrasing of the question, or at least in the way the witness understood the question. Even with the best intentions, it is difficult for an expert witness to avoid hindsight, particularly when that expert has already considered a closely-related item of prior art.

I would nevertheless comment that, in my opinion, explicitly instructing an expert to follow the Pozzoli approach can create a risk of hindsight. The court normally adopts the Pozzoli approach, but it does not follow that it is necessary to instruct the expert to do so. In the present case, for example, there was no room for dispute as to what the difference between RD162 and RD162' was in structural terms (step 3 in Pozzoli). Hindsight would have been easier to avoid if Prof Westwell had been asked an open question along the following lines: supposing that the skilled team, after having read the Poster, wanted to develop an alternative to RD162 which had similar therapeutic potential, what compound(s) would have been obvious choices to investigate? In saying this, I am not intending to be prescriptive about how experts should be instructed, particularly in other kinds of case.

In conclusion, I consider that the judge was entitled to conclude that Prof Westwell’s evidence was infected with hindsight. He certainly made no error of principle in doing so.