MUC4 and familial pancreatic carcinoma: MUC4 was stably down-regulated in CD18/HPAF pancreatic cancer cells, which express high level of MUC4, by MUC4 siRNA and resulting stable transfectant pool (CD18/HPAF/siMUC4) was quantitated for MUC4 expression by immunoblot analysis (Figure 1A).