Rectal Cancer Key Insights — Recognizing Symptoms and Exploring Modern Treatment Options

Differences Between Rectal and Colon Cancer — Location, Structure, and Symptoms

The large intestine consists of the colon and the rectum. Rectal cancer refers to malignant tumors that develop in the final 12–15 centimeters of the intestine, just before the anus. Because the rectum is located very close to the anus and functions as a reservoir for stool, symptoms of rectal cancer — such as blood in the stool and difficulty with bowel movements — often appear earlier than those of colon cancer.

Structurally, the rectum lacks a protective serosal layer and is closely connected to pelvic nerves, blood vessels, and urogenital organs. This anatomical difference means that the growth and spread patterns of rectal tumors can differ significantly from those of colon cancer.

The Development of Rectal Tumors — From Polyps to Cancer (Approximately 10 Years)

Most cases of rectal cancer gradually evolve from benign colorectal polyps (adenomas) on the inner lining of the intestine. The transformation from a benign polyp into a malignant rectal tumor typically takes about 10 years. If polyps are detected and removed through endoscopy during this critical window, the risk of developing cancer can be significantly reduced.

Unhealthy Lifestyle Habits — Obesity, Lack of Exercise, and High Intake of Red and Processed Meats

Hong Kong’s urban lifestyle is often fast-paced, with many people leading sedentary lives and engaging in little physical activity. This can slow down bowel motility and increase the risk of colorectal issues. Moreover, frequent consumption of large amounts of red meat (such as beef and pork) and processed meats (like sausages and luncheon meat) has been identified by the World Health Organization as a significant risk factor for developing colorectal and rectal cancers.

Dietary Factors — Low-Fiber Diet, Smoking, and Alcohol

A long-term diet lacking in high-fiber fruits and vegetables can prolong the retention of harmful substances in the intestine. In addition, smoking and excessive alcohol consumption can damage cells and increase the likelihood of genetic mutations, thereby raising the risk of colorectal and rectal cancer.

Genetics and Family History — FAP and HNPCC (Lynch Syndrome)

Some cases of rectal cancer are closely linked to inherited genetic mutations. For example:

• Familial Adenomatous Polyposis (FAP): Patients develop hundreds to thousands of polyps in the intestine. If these are not removed, there is a very high likelihood that they will progress to cancer.
• Hereditary Non-Polyposis Colorectal Cancer (HNPCC / Lynch Syndrome): This condition significantly increases the likelihood of developing early-onset colorectal and rectal cancer.

Personal Medical History — Ulcerative Colitis, Crohn’s Disease, and History of Colorectal Polyps

Individuals with chronic inflammatory bowel diseases (such as ulcerative colitis or Crohn’s disease), or those with a history of adenomatous colorectal polyps, face a higher risk of developing rectal cancer compared to the general population.

Blood or Mucus in Stool — Difference Between Bright Red and Dark-Colored Blood

One of the most noticeable symptoms of rectal cancer is blood in the stool. Unlike black stools caused by gastric bleeding, rectal cancer — due to its proximity to the anus — often results in stools that contain bright red or dark red blood, sometimes mixed with mucus.

Changes in Bowel Habits — Constipation, Diarrhea, or Alternating Between Both

If unexplained constipation, diarrhea, or alternating episodes of both persist for several weeks, it should be taken seriously as a potential warning sign.

Narrow Stools — From Thick to Thin

As rectal tumors gradually enlarge, they can obstruct the intestinal passage. This narrowing causes stool to become compressed as it passes through, resulting in thinner, pencil-like shapes.

Incomplete Evacuation — Tenesmus

Patients often experience a persistent sensation of “not fully emptying” after bowel movements. Medically, this is referred to as tenesmus, where there is a constant feeling that something is obstructing the rectum, leading to repeated urges to use the toilet even right after defecation.

Iron-Deficiency Anemia — A Warning Sign of Chronic Intestinal Bleeding

Long-term, chronic occult bleeding in the intestine can lead to iron loss, resulting in iron-deficiency anemia. Patients may appear pale and are prone to dizziness.

Abdominal Discomfort — Pain, Cramping, or Bloating

Tumors may trigger intestinal spasms or partial blockages, leading to intermittent cramping pain or persistent abdominal bloating.

Unexplained Fatigue and Weight Loss

As cancer cells grow, they consume a large amount of the body’s nutrients. When significant weight loss occurs without intentional dieting, accompanied by persistent extreme fatigue, it is a warning sign that should prompt early medical consultation.

Survival Rates by Stage — Over 90% in Early Stage, Only Around 10% in Stage IV

According to data from the Hong Kong Cancer Registry, rectal cancer survival rates are closely related to the stage at diagnosis1:

• Stage I: Tumor confined within the intestinal wall, with a five-year survival rate exceeding 90%.
• Stage II: Tumor penetrates the intestinal wall but has not spread to lymph nodes, with a five-year survival rate of about 88%.
• Stage III: Cancer cells have spread to nearby lymph nodes, reducing the five-year survival rate to around 69%.
• Stage IV: Cancer has metastasized to distant organs (such as the liver or lungs), with a five-year survival rate generally below 10%.

Digital Rectal Examination (DRE)

The doctor wears gloves, applies lubricant, and inserts a finger into the patient’s anus to feel for any hard masses or abnormal tumors in the lower rectum.

Fecal Occult Blood Test (FOBT)

By analyzing stool samples, this test detects trace amounts of blood that are invisible to the naked eye, making it an excellent preliminary screening tool.

Sigmoidoscopy

A flexible tube equipped with a camera is used to examine the interior of the rectum and the lower part of the colon (sigmoid colon).

Colonoscopy and Biopsy

This is considered the gold standard for diagnosing rectal cancer. Doctors can directly observe the entire colon and rectum, and if any suspicious tumors are detected, tissue samples can be taken immediately for pathological examination.

CT Colonography

Also known as virtual colonoscopy, this method uses CT scanning technology to reconstruct three-dimensional images of the intestine. It is particularly suitable for patients who are unable to undergo traditional colonoscopy.

Pelvic MRI — Preoperative Assessment for Rectal Cancer

For rectal cancer patients, preoperative pelvic MRI is crucial. It provides precise evaluation of the depth of tumor invasion into the intestinal wall (T staging) and the distance to the circumferential resection margin (CRM), it also detects Extramural Vascular Invasion (EMVI). EMVI is a critical prognostic factor that indicates whether the rectal cancer is prone to distant metastasis (such as liver or lung metastasis). The precise anatomical data provided by pelvic MRI is essential for the Multidisciplinary Team (MDT) to accurately determine whether a patient requires preoperative neoadjuvant therapy, thereby customizing the safest and most personalized curative treatment plan for every patient.

PET-CT Scan — Determining Stage and Extent of Spread

PET-CT is primarily used to assess whether cancer cells have metastasized to distant organs such as the liver or lungs, helping to accurately determine the stage of rectal cancer.

Pre-Treatment Preparation — Imaging Evaluation and Personalized Planning

After diagnosis, a multidisciplinary team of specialists — including surgeons, oncologists, radiologists, and pathologists — collaborates to design the most suitable personalized treatment plan for the patient, based on imaging scan results.

Surgery — Total Mesorectal Excision (TME)

Total Mesorectal Excision (TME) is the current standard surgical procedure for rectal cancer. By completely removing the rectum along with the surrounding lymphatic tissue, it significantly reduces the risk of recurrence.

Minimally Invasive Laparoscopic Surgery and Transanal Total Mesorectal Excision (TaTME)

• Minimally Invasive Laparoscopic Surgery: Smaller incisions, reduced pain, and faster recovery.
• TaTME: Designed for very low rectal tumors, performed simultaneously through the abdomen and anus to improve precision of tumor removal and increase the chance of preserving the anus.

Robotic-Assisted Surgical Resection

Robotic-assisted surgery has become one of the important minimally invasive treatment options for rectal cancer in recent years. With 3D high-definition visualization and robotic arms with 7 degrees of freedom and tremor filtration, surgeons can perform more precise tissue dissection and vessel ligation within the narrow pelvic cavity. This approach is particularly suitable for patients with low rectal cancer or tumors located in complex positions.
Beyond increasing the success of complete tumor removal and sphincter preservation, robotic surgery excels at identifying and preserving the delicate autonomic nerves in the pelvis. This technological advantage significantly reduces the risk of postoperative urinary issues (such as urinary retention) and sexual dysfunction.

Sphincter-Preserving Surgery vs Colostomy (Stoma Bag)

Whether the anus can be preserved depends on the distance between the tumor and the anal sphincter. If the tumor is very close to the anus, complete removal of cancer cells may require excising the anus and creating a permanent colostomy in the abdomen (commonly referred to as a stoma bag) for waste elimination.

Neoadjuvant Therapy — Combined Chemotherapy and Radiotherapy

For stage II or stage III rectal cancer, doctors often recommend a treatment plan that combines radiotherapy with chemotherapy. The goal is to shrink the tumor before surgery, thereby increasing the chances of successful removal and preserving the anus.

Postoperative Adjuvant Chemotherapy and Radiotherapy

After surgery, to eliminate any microscopic cancer cells that may remain in the body, doctors may recommend postoperative adjuvant chemotherapy based on the findings of the pathology report.

Targeted Therapy for Advanced Rectal Cancer — Anti-VEGF and EGFR Inhibitors

For advanced or metastatic rectal cancer, targeted drugs combined with chemotherapy are the main treatment approach. These agents can either cut off the tumor’s nutrient supply (such as anti-VEGF therapies) or block the growth signals of cancer cells (such as EGFR inhibitors).

Latest Applications of Immunotherapy

For rectal cancer patients with specific genetic alterations — such as high microsatellite instability (MSI-H) or deficient mismatch repair (dMMR) — immunotherapy can reactivate the body’s immune system to attack cancer cells, delivering remarkable treatment outcomes.

The above treatment methods represent only some of the common options for rectal cancer and may not be suitable for all patients. Each individual’s condition, tumor location, stage, overall health status, and personal needs vary, so treatment plans must be tailored accordingly. Patients are advised to discuss in detail with their attending physician and make decisions based on professional medical guidance to determine the most appropriate treatment plan for themselves.

Postoperative Bowel Function Adjustment — Potential Intestinal Dysfunction

Even when the anus is successfully preserved, the reduced rectal capacity often leads to Low Anterior Resection Syndrome (LARS), with symptoms such as frequent bowel movements, incontinence, or constipation. These conditions generally improve gradually within several months to a year after surgery.

Postoperative Dietary Progression — Transition from Clear Fluids to Normal Diet

In the early postoperative stage, patients are advised to follow a low-residue diet, avoiding high-fiber, spicy, and gas-producing foods to reduce stress on the intestines. As bowel function gradually adapts, patients can progressively transition back to a normal, balanced diet.

Daily Care and Psychological Support for Stoma Patients

In the early stages of wearing a stoma, patients often experience difficulty adjusting. In Hong Kong, several hospitals and organizations have specialist stoma nurses who provide professional guidance on stoma cleaning and bag replacement, as well as psychological support to help patients adapt to their new lifestyle.

Recommended Rehabilitation Exercises

Once the surgical wound has healed, patients may begin light aerobic exercises such as brisk walking, which help stimulate bowel movement and strengthen overall physical fitness. Activities should be resumed gradually and carefully to avoid overexertion, ensuring a safe recovery process.

Recommended Screening Methods and Frequency — FOBT, Sigmoidoscopy, Colonoscopy

• Fecal Occult Blood Test (FOBT): Recommended once a year.
• Sigmoidoscopy: Recommended every five years.
• Colonoscopy: Recommended every ten years; if polyps are detected, the interval should be shortened as advised by the physician.

High-Risk Individuals Should Undergo Earlier Screening

Individuals with a family history of colorectal cancer or a personal history of polyps should not wait until the age of 50. They are advised to consult their doctor early to determine the appropriate age for screening.

Preparation Before Colonoscopy

Before undergoing a colonoscopy, patients should follow a low‑residue diet for several days and take prescribed laxatives to cleanse the bowel. This ensures the colon is clean and prevents stool from obscuring any polyps.

• Eat more high-fiber foods: Ensure daily intake of vegetables, fruits, and whole grains.
• Reduce red meat consumption: Limit intake of beef, lamb, and processed meats.
• Maintain a healthy weight: Keep a normal BMI through regular exercise.
• Quit smoking and limit alcohol: Avoid carcinogens to protect intestinal health.

Rectal Cancer: Early Symptoms and How to Differentiate from Hemorrhoids

Bleeding from hemorrhoids is usually bright red, often dripping after bowel movements or appearing on toilet paper, and is commonly accompanied by anal pain or itching. In contrast, rectal cancer may present with blood mixed in the stool, which can be either dark red or bright red, and is often associated with changes in bowel habits, narrowing of stool, and systemic symptoms such as weight loss.

Can Hemorrhoids Develop into Rectal Cancer?

No. Hemorrhoids are a benign condition caused by the dilation of anal venous vessels and do not progress into rectal cancer. However, the symptoms of the two conditions can be similar. Persistent bleeding from hemorrhoids may mask the warning signs of rectal cancer, so the presence of ongoing blood in the stool should always prompt medical evaluation.

What Are Colorectal Polyps? How Are They Related to Rectal Cancer?

Colorectal polyps are abnormal growths on the lining of the intestine. Among them, adenomatous polyps carry a significant risk of transforming into rectal cancer over time. Early removal of polyps is one of the most effective methods of cancer prevention.

Do Rectal Cancer Surgeries Always Require a Permanent Stoma?

Not necessarily. A permanent stoma may only be required when the rectal tumor is very close to the anal sphincter (typically less than 2–5 cm), in order to ensure complete removal of the tumor. With advances in medical technology, robotic surgical systems have significantly increased the success rate of sphincter preservation.

Is Chemotherapy Recommended for Rectal Cancer? Under What Circumstances Is It Needed?

Chemotherapy is an important adjuvant treatment. For stage II and III rectal cancer, preoperative chemotherapy (combined with radiotherapy) can help shrink the tumor, while postoperative chemotherapy can eliminate microscopic metastases and significantly reduce recurrence rates. In advanced cases, chemotherapy may also prolong survival and relieve symptoms.

What Treatment Options Are Available for Advanced Rectal Cancer?

Even in advanced stages, multiple treatment options remain available. Targeted therapy and immunotherapy, combined with palliative chemotherapy or surgery, can effectively control disease progression and improve patients’ quality of life.

Can Rectal Cancer Recur After Treatment? How Is Follow-up Done?

There is a risk of recurrence, most commonly within the first two years after surgery. Patients must attend regular follow-up appointments, including carcinoembryonic antigen (CEA) blood tests, colonoscopy, and CT scans, to closely monitor their condition.

Is Rectal Cancer Hereditary? Should I Get Screened If a Family Member Is Affected?

Individuals with a first-degree relative (parents, siblings, or children) who has had colorectal cancer are at a higher risk. It is advisable to start colonoscopy screening ten years earlier than the usual recommended age.