This hypothesis is underscored by our finding that a higher number of circulating tumour cells was observed in the bloodstream of E- and P-selectin-deficient scid mice compared with wild-type scid mice, indicating that E- and P-selectin deficiency affected tumour cells extravasation as in E- and P-selectin-deficient mice, in which an extreme leukocytosis was observed, indicating that the leukocytes were similarly unable to leave the circulation (Frenette et al, 1996). This evidence concerns the gene SELP and neoplasm.