To address this question, we have analyzed the expression of the checkpoint sensors RAD17, RAD9, and ATR, the mediators Claspin and Timeless and the effector CHK1 (Fig. 1a) in 93 primary non–small-cell lung cancers (NSCLC)27, 74 primary colorectal carcinomas41, and 206 primary breast cancers42. The gene discussed is ATR; the disease is lung cancer.