Consistent with the observation that CTCs are heterogeneous in nature and that a specific CTC population isolated by a given method is a predictor for therapeutic response, SMAD4 expression of a CTC population called circulating tumor and invasive cells (CTICs) was able to predict response of pancreatic ductal adenocarcinoma.9 In addition, CTCs expressing fibroblast activation protein alpha (FAPα)/seprase and epithelial cell adhesion molecule are distinct subpopulations of CTCs and the use of these markers in concert could provide information concerning therapeutic response.10 Here, FAP is linked to neoplasm.