Dark stools
The most alarming sign of colon cancer is blood in the stool Sometimes patients notice bright red spots but blood in stool can be invisible to the naked eye. This condition is called occult blood in stool. The severity of symptoms generally depends on the metastasis and location of the malignant cells.
Dark or black stool is also a bad sign for cancer suspected patient signifying the existence of dried blood. A fecal occult test is generally prescribed to the patients which can reveal any blood cells not visible to naked eye. Further examination and lab investigations are ordered to determine source of blood. Consult your doctor immediately so the treatment plan can be formulated.