Colorectal cancer includes tumors that affect part of the large intestine (the colon) and the rectum (end of the intestine, the portion located before the anus). When diagnosed early, it is usually treatable and, in most cases, curable. This is usually possible when it has not yet spread to other organs (called metastasis).
Most of these tumors start from the appearance of polyps, which are benign lesions that can grow on the inner wall of the large intestine.
Rectal cancer itself also starts in the lining cells and starts as a polyp. Its incidence is approximately 29% among intestinal tumors. It is worth mentioning that the rectum is the portion of the large intestine bounded inferiorly by the dentate line. The low rectum is located up to 5 cm from the anal verge, the medium rectum, between 5 and 10 cm from the anal verge, and the high rectum, between 10 and 15 cm from the anal verge.
Data from the latest world estimate indicate that 1 million new cases of colon and rectal cancer were reported in men, being the third most frequent tumor among all male cancers, with an estimated risk of 26.6/100 thousand. For women, this number was slightly lower, with 800,000 new cases being recorded, being the second most frequent tumor, with an incidence rate of 21.8/100,000.
In Brazil, it is estimated that between the years 2018 and 2019, 36,360 new cases of colorectal cancer have arisen, 17,380 in men and 18,980 in women. These values correspond to a risk of 16.83 new cases per 100,000 men and 17.9 per 100,000 women in our country.
In terms of mortality, according to INCA (National Cancer Institute), in 2017, 9,207 deaths from colon and rectal cancer (9.12/100 thousand) were observed in men and 9,660 (9.33/100 thousand) in women.
The incidence of colorectal cancer has a significant increase after the age of 50 and continues to increase with advancing age, although the number of cases has recently increased in younger patients.
The risk factors for rectal cancer, specifically, are closely related to eating and living habits and previous health conditions. Among them, the following stand out:
Diets rich in red meats, processed meats and meats exposed to intense heat;
Diets low in fiber (fruits, vegetables and greens);
Sedentary lifestyle (because obesity is a risk factor, and maintaining regular exercise helps to avoid it);
Chronic inflammatory bowel diseases (such as ulcerative colitis and Crohn’s disease);
Family history of colorectal cancer cases; and
Familial syndromes (especially Lynch syndrome and familial adenomatous polyposis – FAP)
Colorectal cancer subtypes
The vast majority of colorectal tumors are classified as adenocarcinomas. These cancers start in cells that secrete mucus to lubricate the interior of the colon and rectum and have some subtypes, such as signet ring cell and mucinous adenocarcinoma.
Other types of tumor that can start in the colon and rectum include:
- Carcinoid tumors;
- Gastrointestinal stromal tumor (GIST);
- Lymphomas; and
Colorectal cancer symptoms
Colorectal cancer can be a silent disease and not cause immediate symptoms. But when present, they can include:
- Change in bowel habits, such as diarrhea, constipation, or narrowing of the stool, that lasts for a few days;
- Even after evacuation, there is no feeling of relief, it seems that not all fecal content has been eliminated (symptom especially suggestive in cases of rectal cancer);
- Rectal bleeding (blood is usually very red and shiny);
- Presence of blood in the stool, making it dark brown or black;
- Cramping or abdominal pain;
- Feeling of fatigue and weakness; and
- Weight loss for no apparent reason.
Importantly, many of these symptoms can be caused by conditions other than colorectal cancer, such as infection, hemorrhoids, or Irritable Bowel Syndrome. That is why, at the first sign of abnormality, it is important to seek a medical evaluation.
Colorectal cancer diagnosis
The first step in diagnosing colorectal cancer is to trace the patient’s medical history to identify possible risk factors.
The physical examination may include palpating the abdomen for abnormalities, such as enlarged masses or organs. In addition, a digital rectal exam may also be required, in which the doctor inserts a finger (protected by a lubricated glove) into the rectum to see if there are any abnormal areas.
Other tests may be requested in the process of diagnosing colorectal cancer. Are they:
- Stool examination;
- Blood Tests;
- Biopsy; and
- Imaging exams (X-ray, ultrasound, magnetic resonance, computed tomography and PET Scan).
In the diagnosis, the staging of colorectal cancer is also determined, that is, the stage in which the tumor is classified. It is very useful to assist the physician in making treatment decisions. In colorectal cancer, there are four stages:
- Stage I – tumor confined to the mucosa (IA) or the muscular layer (IB) of the colon or rectum and without involvement of the lymph nodes (ganglia);
- Stage II – tumor confined to the serosa that lines the colon or rectum (IIA) or that has reached neighboring organs (IIB), but without involvement of lymph nodes (ganglia);
- Stage III – involvement of lymph nodes near the colon or rectum; and
- Stage IV – involvement of distant organs.
The physician and a multidisciplinary team determine treatment options based on the diagnosis of colorectal cancer.
The main approaches adopted in the management of colorectal cancer are:
- Local treatments – treat the tumor without affecting the rest of the body. They are best indicated in the early stages of the disease (in smaller tumors that have not yet spread/metastasized), but can also be used in other situations. The main types used in colorectal cancer include surgery, ablation, embolization and radiation therapy;
- Systemic treatments – through the use of oral (pills) or intravenous (in a vein) drugs, which are applied directly into the bloodstream. Depending on the type of colorectal cancer, chemotherapy, targeted therapies, and/or immunotherapy may be used.
Primary prevention of colorectal cancer includes measures to decrease the risk of developing the disease, such as:
Adopt a diet rich in fiber, fruits and vegetables;
Reduce the consumption of red meat and animal fat;
Practicing physical activities, since a sedentary lifestyle increases the risk of developing the disease;
Maintain a healthy weight (remembering that obesity is a risk factor for this cancer); and
Avoid smoking and drinking alcohol.