Colorectal cancer represents a significant health concern globally, originating in the large intestine, which includes the colon and rectum. This type of cancer can affect individuals across various age groups, though it is more frequently observed in older adults. Understanding the specific areas within the colorectal region where cancer is most likely to develop is important for effective awareness and medical management. This article explores the most common site for colorectal cancer and related aspects of the disease.
The Most Common Site
Colorectal cancer most frequently originates in the rectosigmoid colon. This region encompasses the sigmoid colon and the rectum. Approximately 55% of colon cancers are found in the sigmoid colon, while nearly 50% of colorectal cancers are located in the rectum.
Understanding Colorectal Cancer
Colorectal cancer begins when cells in the colon or rectum grow abnormally and uncontrollably. Most cases typically originate from growths on the inner lining of the colon or rectum called polyps. These polyps are often benign, but some types, particularly adenomatous polyps, can undergo changes over time and become cancerous.
The large intestine, consisting of the colon and rectum, is a long, muscular tube that absorbs water and electrolytes from digested food, forms stool, and stores waste. The colon is divided into several sections: the cecum, ascending colon, transverse colon, descending colon, and sigmoid colon. The rectum is a distinct segment following the sigmoid colon. Cancer develops when the DNA within cells mutates, leading to uncontrolled cell multiplication and the potential formation of a tumor. If left undetected, these cancerous cells can invade surrounding tissues and potentially spread to other parts of the body.
Why This Location is Common
The rectosigmoid colon is a common site for cancer development due to specific anatomical and physiological characteristics. This segment of the large intestine has a narrower diameter compared to other parts of the colon. As waste material moves through the digestive tract, stool transit tends to slow down significantly in this area. This slower movement means that waste remains in contact with the colon lining for a longer duration. Prolonged contact increases the exposure of the colon wall to potential carcinogens present in the stool.
Furthermore, studies indicate that precancerous polyps, which are precursors to cancer, are often found in greater density within the sigmoid colon and rectum. Tumors developing on the left side of the colon, including the sigmoid, are also known to have specific genetic mutations that can contribute to their formation.
Recognizing Key Symptoms
Colorectal cancer often does not present with obvious symptoms in its early stages, making routine screening important. When symptoms do appear, they can vary depending on the tumor’s size and location within the colon or rectum. Common indicators include:
Changes in bowel habits, such as persistent diarrhea, constipation, or a noticeable narrowing of the stool.
Rectal bleeding or the presence of blood in the stool.
Ongoing abdominal discomfort, which can manifest as cramps, gas, or general pain.
A sensation of incomplete bowel emptying after a movement.
Unexplained weight loss.
Fatigue or weakness, often due to anemia from chronic blood loss.
It is important to seek medical attention if any of these persistent signs are observed, even if they seem minor.
Screening and Early Detection
Regular screening plays an important role in the early detection and prevention of colorectal cancer, especially given its prevalence in the rectosigmoid area. Screening aims to find polyps before they become cancerous or to detect cancer at an early, more treatable stage.
Several methods are available for screening. Colonoscopy is a comprehensive procedure that allows doctors to examine the entire colon and rectum, identify polyps, and remove them during the same procedure. Flexible sigmoidoscopy, a less extensive visual exam, focuses on the rectum and the lower part of the colon, including the sigmoid colon.
Stool-based tests, such as fecal occult blood tests (FOBT), fecal immunochemical tests (FIT), and stool DNA tests (FIT-DNA), check for hidden blood or altered DNA in stool samples. While convenient, abnormal stool test results typically require a follow-up colonoscopy. Screening recommendations generally begin at age 45 for individuals at average risk, but specific guidelines may vary based on personal and family medical history.