A 55-year-old patient presents with symptoms of rectal bleeding, changes in bowel habits, and unexplained weight loss. The attending physician suspects colorectal cancer and decides to perform a colonoscopy to identify the location and extent of the tumor.
Which of the following is the most common site of colorectal cancer?
A. Right colon
B. Transverse colon
C. Left colon
D. Rectum
The correct answer is D. Rectum.
Explanation:
Colorectal cancer can occur in various parts of the colon and rectum, but certain areas are more commonly affected. Here’s why the rectum is the most common site:
1. Rectum (D):
– The rectum is the most common site for colorectal cancer, accounting for approximately 30-40% of cases.
– This high incidence is partly due to the anatomical and functional characteristics of the rectum, which is the final segment of the gastrointestinal tract.
– Symptoms of rectal cancer often include rectal bleeding, changes in bowel habits (such as diarrhea or constipation), and a sensation of incomplete evacuation.
2. Other Options:
– Right Colon (A): Cancer of the right colon (including the cecum and ascending colon) is also common, but it is less frequently the primary site compared to the rectum. It typically presents with symptoms like anemia due to occult bleeding, abdominal pain, and sometimes a palpable mass.
– Transverse Colon (B): The transverse colon is a less common site for colorectal cancer compared to the rectum and right colon. Symptoms can vary but may include abdominal pain and changes in bowel habits.
– Left Colon (C): Cancer of the left colon (including the descending colon and sigmoid colon) is quite common and presents with symptoms such as changes in bowel habits, rectal bleeding, and obstructive symptoms. However, it is still less common than rectal cancer.
In summary, while colorectal cancer can occur throughout the colon and rectum, the rectum is the most common site for this type of cancer.
According to the information provided in the Radiopaedia article on colorectal cancer:
Distribution of Colorectal Cancers
- Rectosigmoid: 55%
- Cecum and ascending colon: ~20%
- Ileocecal valve: 2%
- Transverse colon: ~10%
- Descending colon: ~5%
So the rectum and rectosigmoid junction are the most common locations, accounting for 55% of colorectal cancers. The right colon (cecum and ascending colon) is the next most common site at around 20%.
Therefore, the correct answer is D. Rectum