In order to determine which is the best Rab GTPase to analyze as a surrogate marker for secretion of exosomes by cancer cells, we screened for four Rab GTPases (Rab5, Rab7, Rab27a and Rab27b) using three human PDAC cell lines (PANC-1, BxPC-3 and MIA PaCa-2). Here, RAB27A is linked to cancer.