Final answer:
Changes in bowel habits, particularly the presence of blood in stool, are often the first indication of colorectal cancer. Screening methods like fecal occult blood tests and colonoscopies are essential for early detection and prevention.
Step-by-step explanation:
The first indication of colorectal cancer is often related to changes within the bowel habits. These can manifest as constipation or diarrhea, abdominal cramping, and most notably, blood in stool. Blood can appear in bowel movements as a result of rectal bleeding, a symptom which may be caused by the ulceration of a tumor within the colorectal region. Such bleeding may be visible or occult, meaning that it is hidden within the feces and not readily apparent. Detection methods for colorectal cancer include screening for fecal occult blood and performing colonoscopies, which not only identify cancerous growths and precursor conditions like polyps but also enable their therapeutic removal. As such, the presence of blood in the stool could be indicative of colorectal cancer.