In summary, we found that combination of celecoxib and orlistat significantly aggravated ERS and this was more pronounced in MCC and high MUC2 producing cells (dnTCF4-LS174T exposed to doxycycline) compared to NMCC and low MUC2 producing cancers, and that the mucinous nature of these tumors (excessive MUC2 protein production) was responsible for the high aggravated ERS levels. Here, MUC2 is linked to Merkel cell skin cancer.