The inhibition of PP1 and PP2A is a common mechanism underlying tumour promotion in various organs of rodents: The okadaic acid class compounds, including okadaic acid, dinophysistoxin-1, calyculin A, microcystin-LR, and nodularin, are chemical inhibitors of PP1 and PP2A and induce tumour-promoting activities in mouse skin, rat glandular stomach, and rat liver12. Here, PTPA is linked to neoplasm.