Abbreviations: IQR, Interquartile range; vWF:Ag, von Willebrand factor antigen; vWF:RCo, von Willebrand factor ristocetin cofactor.

52-year-old man. He received bilateral T8-L3 posterior fix- ation due to spinal cord compression. He needed RBC trans- fusion due to intra-operative bleeding, although coagulation factor deficiency was not found. We could not detect a significant association between coagulation factor deficiency and post-operative bleeding in patients with cancer and isolated aPTT prolongation. Our findings demonstrated that the main cause of isolated aPTT prolongation in patients with cancer might be a factor deficiency rather than the presence of an inhibitor such as lupus anticoagulant. In addition, the most commonly deficient factor was coagulation factor XII. In contrast, a previous study investigating the cause of isolated aPTT pro- longation in general patients in an acute care setting demon- strated that the prevalent cause of aPTT prolongation was the presence of lupus anticoagulant (4). When considered with our results, this suggests that the etiology of isolated aPTT prolongation might differ according to the disease subgroup. To our knowledge, the current study is the first to examine and report the cause of isolated aPTT prolonga- tion and the frequency of factor deficiency of the intrinsic coagulation pathway in patients with cancer. Factor XII deficiency, a rare congenital disorder, has spor- adically been reported in case reports worldwide. Moreover, until the current report, there was only one report of three cases with genetically confirmed severe congenital factor XII deficiency in Korean patients (5). Except for sporadic case reports, there have been only a few studies investigating factor XII deficiency in the clinical context. Factor XII defi- ciency is also known to be associated with thromboembolism as well as bleeding risk (6). One Greek report showed that factor XII activity was significantly lower in women who experienced recurrent spontaneous abortion, while all normal controls had normal factor XII activity (7). However, there was no peri-operative thromboembolic event in our study population. Further- more, factor XII deficiency was not associated with post-op- erative bleeding events, though one female patient with mild factor XII deficiency received RBC transfusion after a major operation. Although the degree of factor XII deficiency in our pa- tients with cancer was mild and the definition of the lower limit of normal for factor XII is somewhat variable (54% to 70%) (8, 9), we consider it valuable to report an un- expected high incidence of factor XII deficiency in patients with cancer and isolated aPTT prolongation.