SELP and neoplasm: Although metastases had engrafted in the connective tissue of the alveolar septae in wild-type scid mice, metastases in the E- and P-selectin-deficient scid mice had only grown in the pulmonary arteries and their tributaries (Figure 3A and B) – a rare occurrence in humans – indicating that the metastasising tumour cells were unable to cross the endothelial barrier.