Cancers that can cause bitter mouth include oral cancer, lung cancer, liver cancer and gallbladder cancer. There are many diseases that can cause bitter mouth. Some liver and biliary diseases or oral diseases may cause bitter mouth symptoms, such as cholecystitis, gallstones, mouth ulcers or certain gastrointestinal diseases. If cancer is suspected, the bitterness of mouth caused by malignant tumors in the above mentioned areas should be considered. Usually, the bitterness of mouth caused by malignant tumors is more serious and cannot be relieved even after treatment by various means, such as brushing teeth frequently, chewing gum or using other methods, which may have a certain effect temporarily, but the effect will not last long and the bitterness of mouth will continue after a period of time. However, the effect will not last long and the bitterness will continue to be serious after a period of time. Therefore, if patients have bitter mouth for a long time, they should pay enough attention to it and go to a regular hospital for relevant examination in time to prevent the occurrence of malignant tumor.