Last year's Mayo Collaborative Services v Prometheus Laboratories, Inc (Mayo v Prometheus) decision, from the US Supreme Court, is beginning to spell trouble for the patenting of diagnostic method inventions in the US.  The ruling in that decision indicated that methods involving an application of a law of nature (e.g. something that inherently occurs in the body) may not be patentable, unless further features are present that provide practical assurance that the methods are genuine applications of those laws.  The decision therefore implied that methods of diagnosis which only comprise steps of identifying/measuring a biomarker in a sample (and no other steps of non-conventional nature), may face patentability difficulties in the US.

Unfortunately for companies working in this area, this judgement is being implemented in other more recent decisions from the US courts.  PerkinElmer Inc and NTD laboratories Inc v Intema Ltd concerned a patent directed to non-invasive diagnostic methods for the determining the risk of foetal Down Syndrome, where the levels of at least one marker were measured in the first and second trimesters of pregnancy and the risk of Down Syndrome was evaluated using these measurements.  The Federal Circuit indicated in this case that the relationship between screening marker levels and the risk of Down Syndrome was a law of nature and that the data gathering steps of the method were not sufficient to confer patentability (marker detection was carried out by well-known methods and the risk determining step was a mental act). 

Further, in Aria Diagnostics, Inc v Sequenom, Inc, the District Court refused a preliminary injunction because the alleged infringer raised questions concerning the validity of the patent in view of Mayo v Prometheus.  The patent in this case concerned a method of using cell-free foetal DNA in the blood of a pregnant woman to conduct non-invasive pre-natal tests.

Although the USPTO has published some guidance on the patentability of diagnostic methods in view of Mayo v Prometheus, it is still unclear exactly what requirements need to be met by the method for it to be considered as patentable.  In this respect, in PerkinElmer, the Court hinted that the patent may have fared differently had additional steps been claimed which utilised the data which had been gathered.  In line with this, the guidance from the USPTO indicates that additional steps should be present that integrate the law of nature into the invention to ensure that the claim amounts to significantly more than a law of nature.  However, there is no specific indication of what additional steps could be considered to confer patentability. 

Hence, the situation at the USPTO with regard to the patentability of diagnostic methods remains uncertain.  Whilst there may be some possible (but unconfirmed) ways to address the potential patentability problems (e.g. including a treatment step, or particular regime based on the gathered data, or specifying detection by a non-conventional method), the situation is far from ideal in the US.  Only time will tell to what extent methods of diagnosis remain patentable at the USPTO.