Response.

Abstract

We thank Drs Ferreyro et al for their interest in our article, their insightful comments, and the opportunity to reply. Ferreyro et al published a prognostic score with a final sample of 540 patients with VTE in 2013. Of these patients, 349 (two-thirds) composed the derivation cohort and 191 patients the validation cohort.1 In the derivation cohort, there were 32 cancers (9.2%) diagnosed during 1 year of follow-up. Moreover, they included a secondary analysis evaluating a combined outcome of cancer or death to address the possibility that death might occur before the identification of an occult cancer. In our opinion, this analysis should be taken with caution, because it is very difficult to assume that all deaths are secondary to occult cancer. In our study, 444 patients (7.6%; 95% CI, 6.90-8.28) were diagnosed with cancer beyond the first 30 days with a follow-up 2 years.2 One of the major differences with the study by Ferreyro et al is the sample size. As we know, the choice of an adequate sample size for a Cox regression analysis is generally based on the rule of thumb derived from simulation studies of a minimum of 10 events per variable.3 In the multivariate model, the authors included 3 variables, obtaining for previous VTE ß: 64 (95 CI%, 7.07-579).1 This large CI suggests that these data are not robust, mostly resulting from few events.