In a similar vein, Ihle and colleagues noted that mutant PIK3CA and loss of PTEN activity were sufficient, but not necessary, as predictors of sensitivity to the anti-tumour activity of the PI3K inhibitor PX-866 in vivo in the presence of wild-type RAS, whereas mutant oncogenic RAS was a dominant determinant of resistance, even in tumours with coexisting mutations of PIK3CA [135]. Here, PTEN is linked to neoplasm.