ABCB1 and colon mucinous adenocarcinoma: MDR1 expression was observed in well‐differentiated and moderately differentiated mucinous adenocarcinomas in all seven cases (100%); MDR1 expression was also detected in serous adenocarcinoma and clear cell carcinoma in five of 13 cases (38.5%) and six of 15 cases (40.0%), respectively.