What are the symptoms of colorectal cancer and how to diagnose it?

In addition to early colorectal cancer, which may have an insidious onset and no symptoms, advanced colorectal cancer often has clinical manifestations of varying degrees. At this time, as long as you are vigilant, ask about the medical history in detail, conduct a careful physical examination, and supplement with laboratory, endoscopic and X-ray examinations, it is not difficult to make a correct diagnosis. Detailed inquiry into the medical history can often reveal the diagnosis of colorectal cancer. People over middle age who have unexplained weight loss, anemia, changes in bowel habits, mucus in the stool, blood in the stool, intestinal obstruction, etc. should consider colorectal cancer.

In addition to the early stage of colorectal cancer, which may have an insidious onset and no symptoms, advanced colorectal cancer often has clinical manifestations of varying degrees. At this time, as long as you are vigilant, ask about the medical history in detail, conduct a careful physical examination, and supplement with laboratory, endoscopic and X-ray examinations, it is not difficult to make a correct diagnosis.

1. Medical history

A detailed medical history can often reveal the diagnosis of colorectal cancer. For those who are middle-aged or older and have unexplained weight loss, anemia, changes in bowel habits, mucus in stool, blood in stool, intestinal obstruction, etc., the possibility of colorectal cancer should be considered. In order to detect colorectal cancer early, some people who have no obvious symptoms but have risk factors for colorectal cancer, such as those with a family history of colorectal cancer, those who have suffered from multiple polyposis of the colon, ulcerative colitis, Crohn's disease, chronic schistosomiasis, or those who have received pelvic radiotherapy or cholecystectomy, should be followed up and reexamined regularly.

2. Physical Examination

A comprehensive physical examination not only helps to correctly diagnose colorectal cancer, but also estimates the severity of the disease, the invasion and metastasis of cancer, and serves as a reference for formulating a reasonable treatment plan. Local signs should pay special attention to intestinal obstruction, abdominal mass, and abdominal tenderness. Since the vast majority of colorectal cancers occur in the rectum and sigmoid colon, a digital rectal examination should be essential. Whenever a patient has symptoms such as blood in the stool, changes in bowel habits, and deformed stools, a digital rectal examination should be performed. During the examination, find out whether the anus or rectum is narrowed, whether the finger cuff is stained with blood, and if a mass is touched, its location, shape, range of lesions, activity of the base, and its relationship with adjacent organs should be clarified.

3. Evaluation of early diagnosis of colorectal cancer and population screening

As mentioned above, the incidence of colorectal cancer has been increasing year by year, with a high mortality rate, and the 5-year survival rate is closely related to the Dukes stage. Since the cause of colorectal cancer is unknown, the improvement of survival rate depends on secondary prevention, that is, early diagnosis of colorectal cancer. Early diagnosis includes two meanings: one is early detection, and the other is early diagnosis. At present, due to the widespread use of fiber colonoscopy, endoscopic pathological tissue sampling and biopsy have become very simple and easy, so it is not very difficult to diagnose precancerous lesions or early cancer. However, the early detection of colorectal cancer still faces many obstacles. The main reason is that the symptoms of early colorectal cancer are often hidden, and patients who come to the doctor are often in the late stage of cancer; in addition, there is currently a lack of specific laboratory examination methods for early cancer diagnosis.

An important way to detect early cancer is to conduct a census of asymptomatic people or monitor patients with a family history of colorectal cancer or confirmed precancerous lesions. Since the diagnosis of cancer often depends on fiber colonoscopy and pathological biopsy, any form of census must take into account workload, economic costs and social tolerance. Conducting initial screening tests to reduce the number of high-risk groups can make up for the shortcomings of fiber colonoscopy in application. Even if the screening efficiency is considered alone, the initial screening test can improve the detection effect of fiber colonoscopy. For example, in a census of more than 10,000 people, we compared the results of simple sigmoidoscopy and immune occult blood-colonoscopy sequential census and found that after the initial screening test, the detection rate of cancer by sigmoidoscopy can be increased from 0.14% to 0.43%.

As a primary screening test for colorectal cancer, the method must not only be sensitive and specific, but also simple, easy to use, economical and practical. So far, many methods have been tried for experimental diagnosis of colorectal cancer, but most of them are difficult to meet the above requirements. This is because most diagnostic indicators only have average differences between colorectal cancer patients and control patients, but they are not specific, it is difficult to establish the diagnostic threshold of cancer, and they are often insensitive to early cancer. According to the colorectal cancer survey data worldwide, the primary screening tests currently used for surveys are mainly fecal occult blood tests and rectal mucus T antigen tests developed in recent years. In addition, the use of monoclonal antibodies to detect colorectal cancer-related antigens in blood or feces is being tried in a small range of survey populations.

There are many methods for fecal occult blood tests. The chemical occult blood test method is simple, but it is easily affected by many factors and may result in false positives (such as eating meat, fresh fruits, vegetables, iron supplements, aspirin, etc.) and false negatives (such as long-term retention of feces, decomposition of hemoglobin in the intestinal cavity, and taking antioxidants such as vitamin C, etc.). Immunoassay is the second generation of colorectal cancer screening test after the chemical occult blood test. Its outstanding advantages are strong specificity and no interference from food and drugs. The early research was the agar immunodiffusion method, but we found in the application that although the specificity of this method is good, its sensitivity for cancer detection is not superior to that of the chemical method. Subsequently, we compared the reverse indirect hemagglutination test, the immune latex test, and the SpA coagulation test. The principle is to coat human hemoglobin antibodies on a carrier. The results showed that the SpA immune occult blood test can greatly improve the sensitivity and specificity of occult blood detection. In the 8233 cases surveyed, we found 934 positive patients, of which 4 cases of colorectal cancer were detected, and 3 were early cancers. It is worth mentioning that the SpA test uses staphylococci containing A protein as a carrier. The antibody labeling does not require purification or complicated processing. During the operation, only a drop of fecal fluid needs to be collected on site and mixed with the SpA reagent. Stable results will appear within 1 to 3 minutes, so it is very suitable for censuses.

It is worth noting that fecal occult blood tests detect colorectal cancer based on intestinal bleeding. Therefore, colorectal cancer patients with no bleeding or only intermittent bleeding may be missed. Many non-neoplastic intestinal bleeding may have false positive results. We found 5 cases of colorectal cancer during an endoscopic survey of more than 3,000 people over the age of 40, including 2 early cancers with negative occult blood tests. Among the patients with positive occult blood, more than 97% had non-neoplastic bleeding. In addition, there is still a problem of the appropriate ratio of reactions in the immune occult blood reaction. False negative results may occur if there is too much blood or an excess of hemoglobin molecules in the stool, which is the so-called "prozone" phenomenon.

In order to overcome the shortcomings of the occult blood test, in recent years, Shamsuddin et al. in the United States proposed the feasibility of rectal mucus galactose oxidase test for screening colorectal cancer (abbreviated as Shams' test) based on the feature that colorectal cancer and precancerous lesions can show similar T antigen expression in mucosa. We are the first in China to verify the screening effect of this method on colorectal cancer and improve the method so that it can be used for large-scale population screening. The results showed that its positive rate for clinical colorectal cancer detection was 89.6%. We used the Shams' test in a survey of 3820 people over 40 years old and compared it with the SpA immune occult blood test. The results showed that the former had a positive rate of 9.1% and a lesion detection rate of 12.7%, including 2 cases of early cancer and 28 cases of adenoma, which had a significant complementary effect on lesion detection with the SpA test.

Finding a more sensitive and specific colorectal cancer screening test method is one of the important topics in colorectal cancer prevention and treatment. Recently, it was reported that the mutation of the ras oncogene can be detected from the stool of colorectal cancer patients, but it is too early to apply this research result at the genetic level to clinical practice. The current research mainly uses the existing screening test to optimize the screening program. In the future, colorectal cancer screening may no longer be a simple colonoscopy or occult blood-colonoscopy sequential screening, but based on the sensitivity, specificity, economy of various experiments, as well as the acceptability of the subjects and the social tolerance, the comprehensive and complementary experimental screening tests will improve the screening effect of colorectal cancer.

The early symptoms of colorectal cancer are not obvious, and may be asymptomatic or only vaguely uncomfortable, indigestion, occult blood, etc. As the cancer progresses, the symptoms gradually become more obvious, manifested as changes in bowel habits, blood in the stool, abdominal pain, abdominal mass, intestinal obstruction, and systemic toxic symptoms such as fever, anemia and weight loss. Tumor infiltration and metastasis may also cause changes in corresponding organs. Colorectal cancer presents different clinical signs and physical signs depending on its primary site.

1. Right colon cancer

The prominent symptoms are abdominal mass, abdominal pain, and anemia. Some patients may have mucus or mucus-bloody stools, frequent bowel movements, abdominal distension, intestinal obstruction, etc., but these symptoms are much less common than those of the left colon. The right colon has a wide intestinal cavity, and the primary cancer has often grown greatly by the time it is discovered. Ulcers and masses are common, and many patients can feel a mass in the right abdomen. Unless the tumor directly affects the ileocecal valve, intestinal obstruction is generally rare. Since the stool is still semi-fluid and thin in the right colon, the bleeding caused by the stool rubbing against the cancer is relatively small. Most bleeding is caused by necrotic ulcers of the tumor. Because the blood and fecal fluid are evenly mixed and not easy to detect, it can cause long-term chronic blood loss. Patients often seek medical treatment due to anemia. Abdominal pain is also common, often dull pain, mostly caused by the invasion of the tumor wall by the mass. Secondary infection of cancerous tumor ulcers can cause local tenderness and systemic toxemia.

2. Left colon cancer

The prominent symptoms are changes in bowel habits, mucus and blood in the stool, intestinal obstruction, etc. The left colon cavity is narrow, and primary cancer often grows in a ring-shaped infiltration, which can easily cause intestinal constriction, so constipation is common. Subsequently, due to the increase in fluid accumulation in the upper intestinal cavity and hyperperistalsis, diarrhea may occur after constipation, and the two often appear alternately. Since the stool gradually changes from a paste to a clumpy state when entering the left colon, it is common to see blood in the stool caused by the friction of the stool with the lesion. Patients often seek medical treatment earlier, and anemia caused by long-term chronic blood loss is not as prominent as in the right colon. Intestinal obstruction caused by cancer infiltration around the intestinal wall and stenosis of the intestinal cavity is mostly chronic and incomplete. Patients often have long-term constipation and paroxysmal abdominal pain. Since the obstruction site is relatively low, vomiting is often not obvious.

3. Rectal cancer

The prominent symptoms are blood in the stool, changes in bowel habits, and concomitant symptoms caused by infiltration of advanced cancer. The site of carcinoma in situ is low, and the feces are hard. The tumor is easily rubbed by the feces and easily causes bleeding, which is mostly bright red or dark red, and does not mix with the formed feces or is attached to the surface of the feces column, misdiagnosed as "hemorrhoidal bleeding". Due to the stimulation of the lesion and the secondary infection of the mass ulcer, the defecation reflex is constantly induced, which is easily misdiagnosed as "bacillary dysentery" or "enteritis". The ring-shaped growth of the tumor causes the intestinal cavity to narrow, which is manifested as deformation and thinning of the feces column in the early stage and incomplete obstruction in the late stage.

4. Tumor Infiltration and Metastasis

Local extension is the most common form of infiltration of colorectal cancer. Tumor invasion of surrounding tissues often causes corresponding symptoms, such as rectal cancer invasion of the sacral plexus causing persistent pain in the lower abdomen and lumbosacral region, anal incontinence, etc. Due to the implantation and shedding of cancer cells, a mass may be palpated in the vesicorectal fossa or uterine rectal fossa during rectal examination. Ascites may occur in cases of extensive dissemination. Early cancer may also spread along the lymphatic spaces around the intestinal wall nerves, and then transfer to the lymph nodes through the lymphatic vessels. When cancer cells are transferred to the para-aortic lymph nodes and enter the chylous cisterna, they may metastasize to the left supraclavicular lymph nodes through the thoracic duct, causing enlargement of the lymph nodes there. In a small number of patients, the ascending lymphatic vessels are blocked by cancer thrombi, causing cancer cells to spread retrogradely, resulting in countless diffuse nodules in the perineum. In female patients, the tumor may metastasize to both ovaries, causing Kruken-berg's disease. Advanced colorectal cancer may also metastasize to the liver, lungs, bones, etc. through the blood.

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