Acquired factor IX inhibitor in a patient with adenocarcinoma of the colon.

The association of an acquired inhibitor to factor IX and adenocarcinoma of the sigmoid colon is reported here for the first time. Unlike the lupus anticoagulant, the inhibitor identified did not exhibit marked prolongation of the clotting time using a highly diluted thromboplastin nor was the kinetic behavior of the inhibitor-factor IX interaction time-dependent. Administration of prednisone was associated with the return of the activated partial thromboplastin time to normal values, at which time the tumor was excised and corticosteroids discontinued with no evidence of subsequent factor IX inhibitor activity.