This is crazy:
The case focuses on a patent that covers the concept of adjusting the dosage of a drug, thiopurine, based on the concentration of a particular chemical (called a metabolite) in the patient's blood. The patent does not cover the drug itself---that patent expired years ago—nor does it cover any specific machine or procedure for measuring the metabolite level. Rather, it covers the idea that particular levels of the chemical "indicate a need" to raise or lower the drug dosage.
The patent holder, Prometheus Labs, offers a thiopurine testing product. It sued the Mayo Clinic when the latter announced it would offer its own, competing thiopurine test. But Prometheus claims much more than its specific testing process. It claims a physician administering thiopurine to a patient can infringe its patent merely by being aware of the scientific correlation disclosed in the patent—even if the doctor doesn't act on the patent's recommendations.
The main problem is that the really bizarrely overreaching patent claims are making both the lawyers and the judges focus on how broad the patent is, rather than the implications of medical patents in general. In a sense, the crazy patent is making "normal" medical patents seem reasonable, even though the latter isn't obviously reasonable at all.