Homogeneously intact DPC4 expression in the primary pancreatic cancer cell lines, which were obtained from cancer tissues with intratumoral DPC4 heterogeneity, can be explained by the positive selection of DPC4-expressing cancer cells during primary cell culture or most DPC4 expressing cancer cells presented in cancer tissues specimens at the time of primary cell culture (Fig. 8). Here, SMAD4 is linked to cancer.