Histopathological examination showed that after IR treatment, sensitive PDXs contained only small portion of ESCC cells; however, resistant PDXs remained substantially more cancer cells, with the amount of Ki67-positive cancer cells being significantly higher in resistant PDXs than that in sensitive PDXs (Fig. 1c and Supplementary Fig. S1a). Here, MKI67 is linked to esophageal squamous cell carcinoma.