Priority entitlement and sufficiency of disclosure – T 883/23

In T 883/23, the Board of Appeal emphasised that compliance with the requirement of “the same invention” of Article 87(1) EPC is not merely a matter of direct and unambiguous disclosure in the priority application - notably, the claimed subject matter must have also been sufficiently disclosed in the earlier application.

Background

Claim 1 of the Main Request was generally directed to liposomal irinotecan for use in the treatment of metastatic adenocarcinoma of the pancreas.  The treatment included administering 60 mg/m2 of liposomal irinotecan, 60 mg/m2 of oxaliplatin, and two other drugs in specific dosages.

The priority application

The priority application described a dose escalation/de-escalation study using five alternative dosage regimens of irinotecan and oxaliplatin, as shown in the table below.  The purpose of the study was to evaluate safety and tolerability of the treatment. Importantly, this was merely an outline, i.e. the priority application did not describe the results of the study.

The starting point of the study was to be the dose combination in level 1, i.e. a treatment including 80 mg/m2 of liposomal irinotecan (a higher dose than that of claim 1 of the Main Request) and 60 mg/m2 of oxaliplatin.

The intention was to escalate the dose to level 2, and to de-escalate to levels -1/-2 were the dosage regimens of levels 1 or 2 to be found not tolerable.

As can be seen from the table above, the dosage regimen of claim 1 of the Main Request was disclosed as level -1 (i.e. a de-escalated dose).

Claim 1 of the Main Request at least arguably had basis in the priority application, via combination of claim 1, some dependent claims and parts of the description.

Importantly, claim 5 of the priority application disclosed two alternative dosages of irinotecan (60 and 80 mg/m2) and claim 8 defined three alternative dosages of oxaliplatin (60, 75 and 85 mg/m2). 

As far as those two claims were concerned, selections were required to arrive at the dosage of claim 1 of the Main Request.

Independent claim 22 referred to 80 mg/m2 of liposomal irinotecan and 60 mg/m2 of oxaliplatin (cf. level 1 in the table above).

The patent

The patent in suit included the results of the escalation/de-escalation study, according to which the dose level of the starting point for the study (level 1) turned out to be intolerable in human patients, i.e. unsuitable for the intended medical indication.  Meanwhile, the de-escalated level -1 (that of claim 1 of the Main Request) was found to be tolerated.

The reasoning of the Board

The Opposition Division was happy with priority entitlement based on the apparent “clear and unambiguous disclosure” of the claimed subject matter.  In particular, the OD considered that the table of dosage regimens in the outlined escalation/de-escalation study provided “further support that the claimed dosage combination is specifically exemplified”.

The Board, however, took a different view, focusing less on the disclosure of the subject matter and giving more weight to the results of the escalation/de-escalation study as disclosed in the patent (and lack of those results in the priority application).

The Board said that the technical information concerning tolerability of the claimed dosage regimen and intolerability of alternative dosages foreshadowed in claims 5 and 8 of the priority application was not derivable from the priority document; in particular, the mere outline of the escalation/de-escalation study could not provide this information. Thus, the priority document did not substantiate which (if any) dosage combinations were suitable for the claimed medical indication.

The patentee argued that the priority application provided an adequate pointer towards the dosage regimen of claim 1 of the Main Request, since the skilled person would understand that the disclosed combination of lower doses was the most likely to be tolerable.

The Board considered that the study as described in the priority application contained merely “a conditional proposal for the use of a combination of 60 mg/m2 liposomal irinotecan and 60 mg/m2 oxaliplatin [that of claim 1 of the Main Request] as part of a study still to be carried out”.   According to the Board, this “conditional proposal” could not be considered to provide any pointer to the claimed combination of dosages which was “uniquely tolerable”.

The patentee further argued that the priority application described the same subject matter as that of claim 1 of the Main Request, such that priority entitlement should have been acknowledged, irrespective of any additional technical effects which may have been described in a subsequent application.

The Board first said that attaining the claimed therapeutic effect was a functional technical feature of the claim, and that tolerability of the treatment (a prerequisite for therapeutic efficacy) was relevant in this context; however, again, the information concerning tolerability/intolerability of the relevant dosages was not directly and unambiguously derivable from the priority application.

The Board also acknowledged that, to comply with the requirement of “the same invention” (Art. 87(1) EPC), the subject matter claimed in a subsequent application must be directly and unambiguously derivable from the priority application (G 2/98).  That said, the Board emphasised that the mere fact that the claimed subject matter is so derivable does not necessarily mean that the priority claim is valid, irrespective of any technical information associated with the claimed subject matter, which is only described in the subsequent patent application.  Notably, the claimed subject matter must have also been sufficiently disclosed in the earlier application.

Conclusion

In this case, given the lack of the results of the study in the priority document, the priority claim was found to be invalid.

T 883/23 serves as a helpful reminder that, for second medical use filings, it is necessary to substantiate the suitability of the product for the claimed therapeutic application, by way of suitable data and/or common general knowledge. The decision also contains some useful comments on the nature of a ‘pointer’ to a particular combination of features (in this case at least, a “conditional proposal” could not be considered such a pointer).

If you have any questions about EPO practice, feel free to get in touch.  

This article is for general information only and is not intended to constitute legal advice. If you would like tailored advice on a specific matter, please do not hesitate to contact me.