These results reinforce our previous findings by demonstrating that glioblastomas undergo tumour self-seeding [34], a phenomenon previously associated with cancer progression and aggressiveness [27,30,36] Calculation of the labelled numbers detected in the unlabelled tumours by using our previously described method [34] found 3.2 ± 0.2 cells/10 mg sample in Ad-CMV-Tom-treated mice and 2.6 ± 0.2 cells/10 mg sample in Ad-Smad6-treated mice, potentially representing a slight reduction in tumor self-seeding, although this possible difference was not statistically significant (Fig. 6D).. Here, SMAD6 is linked to cancer.