When cancer is present in the body, it may manifest itself through darkening of the skin as well as feces, but it is not limited to three places, and it cannot be said that a darkening in one place is necessarily cancer. If cancer of the gastrointestinal tract occurs, it may cause darkening of the stool. Hepatobiliary cancer as well as pancreatic cancer may manifest as darkening of skin folds, and patients with liver cancer may also have darkening and yellowing of the face. If black patches suddenly appear on the skin, one should also be highly alert to malignant melanoma.1. Darkening of stool: Mostly seen in stomach cancer, small intestine cancer, etc. Because of the long distance of the cancer from the anus, the cancer bleeds less and slower, and it is mixed with food residue, which can be excreted with stool, because the blood stays in the gastrointestinal tract for too long, the blood oxidizes, thus manifesting as black stool, which is attached with mucus and shiny, similar to tar-like. It is also called tar stool. 2. Darkening of skin: If the skin folds are darkened, it can be caused by endocrine disorder due to tumor growth, which can be seen in pancreatic cancer, liver cancer, bile duct cancer, etc. It is manifested as brown-black or gray-black skin folds in armpits, back of neck, groin, etc., and thickened and rough skin. In addition, in the case of liver cancer, patients tend to have dark and yellow face. In case of black patches on the skin, especially when black patches appear suddenly or when the original mole changes in size, color and boundary, the possibility of malignant melanoma should be suspected. Therefore, if the above blackening performance or other abnormal symptoms appear in the body, it is necessary to be highly alert to the presence of lesions in the organism, and it is recommended to actively seek medical examination to clarify the diagnosis.