A low level of CA I in colonic epithelial cells was found to be a specific marker for the prediction of colorectal cancer.18 On the other hand, CA I was highly expressed in the sera of patients with stage I non‐small cell lung cancer (NSCLC).19 Even the plasma of patients with prostate cancer contains an increased level of CA I compared with healthy controls.20 Thus, the elevated level of the CA I protein in the plasma or serum may represent a promising biomarker for both prostate cancer and early stage NSCLC. Here, CA1 is linked to lung cancer.