The Federal Circuit’s recent decision in Medtronic v. Edwards Lifesciences highlights the importance of maintaining accurate priority claims in patent applications, particularly those with multiple generations of priority.

In Medtronic, the asserted patent claimed priority to a French application (application A) an international application (application B), and a series of three U.S. applications (applications C, D, and E). While the priority claim was stated correctly in the asserted patent, the priority claims in the earlier-filed U.S. applications contained various deficiencies. For example, application D incorrectly stated that it was a continuation-in-part of application B, skipping over intervening application C. Apparently, the applicant had reused the priority language from application C when filing application D, without updating the priority claim to include application C. Application E suffered from the same defect (skipping intermediate applications C and D and instead incorrectly stating that it was a continuation-in-part of application B).

In the end, even though the asserted patent properly recited the complete priority chain, the court held that it was not entitled to the earlier filing date of applications A and B due to the defective priority claims in the intermediate applications. Applications A and B were thus treated as prior art with respect to the asserted patent, resulting in a finding of invalidity.

There are a number of important lessons to be learned from this case. First, it is imperative that priority language be stated accurately and updated when filing continuing applications. The U.S. Patent and Trademark Office recently amended 37 CFR 1.78(a)(3) and 37 CFR 1.78(d)(2) to require that all priority claims be stated on an Application Data Sheet (Form PTO/AIA/14), which should help reduce the risk of a “recycling” problem like that encountered in Medtronic.

Another takeaway is that, when evaluating patents for possible invalidity positions, it is important to look not only at the priority claim of the subject patent, but also that of all patents/applications to which the subject patent claims priority. Such a review may lead to discovery of a “Medtronic-type” issue with the priority claim that could result in an invalidity finding.