ALDH (spot no. 16610) was also increased in the spheres, consistent with increased ALDH activity in the serum of patients with PDAC; ALDH activity is also enhanced in the tumor-initiating population related to CD133 or CD44 and contributes to chemoresistance and radiation resistance in pancreatic cancer, breast cancer, and lung cancer [36–39]. Here, CD44 is linked to lung cancer.