The IF revealed that integrin β1–expressing CDX cells formed multicellular hollow tubules that interact with an outer glycoprotein-rich Matrigel shell labeled by lectin that is not present within the tubule lumen (Fig. 6J), further supporting a functional role of integrin β1 in hollow tubule formation by SCLC non-NE cells. This evidence concerns the gene ART4 and small cell lung carcinoma.