With great interest we have read the article by Hovaguimian et al. regarding the effect of different anesthesia drugs (sevoflurane or propofol) on the number of circulating tumor cells in patients undergoing breast cancer surgery. We appreciate and congratulate the authors for setting up a meaningful randomized, controlled trial and sharing such useful findings. There are, however, two important points of concern.

First of all, the study used a mixed Poisson model. However, we noted that the first quartile of circulating tumor cell count results at all time points was zero, and the median was also zero in the 48-h sevoflurane group and the 72-h propofol group, so it was reasonable to assume that there were many zeros (at least 25 to 50%). Therefore, a zero-inflated Poisson regression model2,3  should be adopted when...

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