Before Lourie, Dyk, and Prost. Appeal from the United States District Court for the Eastern District of Virginia.
Summary: A solution to a problem can be obvious even when the problem itself was unknown in the prior art.
ImmunoGen filed a civil action in district court under 35 U.S.C. § 145 to obtain a patent directed to a cancer treatment method using an immunoconjugate drug known as IMGN853. The applied-for claims recited a specific dosage of 6 mg/kg of the patient’s adjusted ideal body weight (AIBW), which the patent explained could avoid the negative side effect of ocular toxicity. After a bench trial, the district court found the claims obvious over ImmunoGen’s own prior art that disclosed dosing IMGN853 based on total body weight (TBW) in view of prior art disclosing dosing based on AIBW. The district court also held the claims were indefinite because the application did not define how to calculate AIBW and there were multiple known formulas for doing so.
On appeal, ImmunoGen argued that the district court erred in finding a motivation to combine the prior art because, at the time of the invention, it was not known that IMGN853 caused ocular toxicity in humans. The Federal Circuit explained, however, that even if the specific problem the inventors purported to solve via the dosing regimen was unknown, that did not necessarily mean that the dosing regimen itself was not obvious. The Federal Circuit found no error in the district court’s analysis because although IMGN853 was not known to cause ocular toxicity, ocular toxicity was a well-known side effect of administering immunoconjugates that contain a drug known as DM4. And because IMGN853 contains DM4, a person of ordinary skill would have understood the potential risk of ocular toxicity and monitored for it when testing IMGN853. Moderating the dosage to avoid the problem therefore would have been obvious.
ImmunoGen also argued that it would not have been obvious to base the dosage on the patient’s AIBW, as opposed to using the patient’s TBW. But the Federal Circuit rejected that argument because the prior art disclosed a dose of 6 mg/kg TBW and, for some patients, their AIBW is the same as their TBW. Thus, the Federal Circuit affirmed the district court’s decision that the claims were obvious and did not reach ImmunoGen’s arguments regarding indefiniteness.
Editor: Sean Murray
