Evidence that Pa ExoS-GAP activity can discriminate differences in Rho GTPases in tumor cells, beyond Rho or Rac activation, was provided by IF studies, which found MTC cells to contract but retain stably adhered branched actin filaments in response to Pa ExoS-GAP, which contrasted with the response of MTLn3 cells, where leading edge architecture was replaced with actin microspikes. Here, RHO is linked to medullary thyroid gland carcinoma.