Last week, in Cancer Research Technology Ltd. v. Barr Laboratories, Inc. (2010-1204), an evenly divided Federal Circuit sitting en banc let stand its prior decision narrowing the doctrine of prosecution laches. The narrowed test requires both a showing of delay during prosecution and prejudice as shown by intervening rights arising during the delay. In so doing, the Federal Circuit rejected its own totality of the circumstances test, recently enunciated in Symbol Technologies, Inc. v. Lemelson Medical, Education, & Research Foundation.

The application for the patent in Cancer Research was originally filed on August 23, 1982, by a British pharmaceutical company. The specification identified and characterized 13 tetrazine compounds, including one named temozolomide. The specification stated that these derivatives possessed anticarcinogenic activity in several animal models.