When results were analyzed regarding cells as primary or metastatic cancer cells based on their origin, we found that cancer cells taken from primary tumor sites tend to show a decrease in SphK1 expression in stiff substrate, whereas cancer cells taken from metastatic sites (e.g. MDA-MB-231 from pleural effusion; H1299 from lymph nodes), showed an increase in SphK1 expression in stiff substrate. Here, SPHK1 is linked to Pleural effusion.