April 6, 2024 

As part of a continuous initiative on cancer awareness and the month March being Colorectal cancer awareness month, in this article I would be focusing on the Colorectal cancers and more specifically on rectal cancer. The reason being, the difference in the approach in colon and rectal cancer treatment protocols, increase in the incidence of the rectal cancer and more importantly to clear the myths associated with the rectal cancer treatment, quality of life and stoma (colostomy/ileostomy) care. 

In 2023, an estimated 153,020 people diagnosed with colorectal cancer worldwide, and there are more than 1.4 million colorectal cancer patients and survivors living today. Colorectal cancer is considered as the second deadliest cancer in the United States. Likewise its incidence is continuously on the rise in India, one of the research papers mentioned that from 2004 to 2014, the colorectal cancer incidence has increased to over 20% and currently 4 - 6 men in 1,00,000 population while 4-5 women in 1,00,000 population are diagnosed with colorectal cancers in India. The increase trend is postulated to be due to change in our lifestyle and food habits. Colorectal cancer is one of the few cancers however that can be prevented with screening. Screening can help find warning signs of colon and rectal cancer early, when treatment is most effective. So it necessary to understand the signs and symptoms of colon or rectal cancer and approach for the necessary for the cure. But first, let’s understand the anatomy of rectum which would make us understand the signs and symptoms easy. 

Anatomy

Gastrointestinal tract in humans starts with the esophagus (food pipe) which continues as stomach, which acts like a reservoir to store food for few hours and then this continues to form small intestine whose length varies from 10-16 feet or 3 to 5 meters inside the abdomen. Small intestine joins to the large intestine at ileocecal junction to form large intestine or colon. Colon is almost 5 feet long (1.5 meters) and is divided into caecum, ascending colon, transverse colon, descending colon and sigmoid colon. Sigmoid colon continues to form rectum which is 12 to 15 cm in length and then ends in anal canal which is 4 cm in length and has got sphincters which control the passage of stools and flatus (Figure 1). Appendix lies at the base of the caecum close to ileocecal junction. Knowledge of length of the rectum and anal canal is important because resection of the rectum and type of surgery performed is based upon on the site of the tumour and the distance of the rectal cancer from the anal verge/sphincter. Another determinant factor in the management of Carcinoma Rectum is the fat and fascia that covers the rectum which is termed as mesorectal fat and mesorectal fascia respectively (Figure 1). As I had mentioned in my Decoding Cancer Article, the carcinoma usually spreads to the regional lymph nodes first, distant nodes later and finally ends up with hematogenous or spread through blood ending with metastasis to distant organs. Likewise, in carcinoma rectum the regional nodes refers to the mesorectal nodes which lies the mesorectal fat enclosed by the mesorectal fascia (Figure 2) and later it spreads to the inferior mesenteric nodes located close to inferior mesenteric artery (main arterial supply to the distal third of transverse colon, descending colon, sigmoid and rectum). Beyond this fascia, rectum is surrounded by pelvic walls laterally and sacrum posteriorly. In males, urinary bladder, prostrate and seminal vesicles lies anteriorly. While in females, uterus and vagina lies in between urinary bladder and rectum. Sympathetic Nerve supply regulating the anal and bladder sphincters arise close to the inferior mesenteric artery origin and descends downwards to receive parasympathetic nerve supply from the sacral foramen and ends up joining the anal and bladder sphincter. The most important it lies just posterior to the inferior mesenteric arteries, so during dissection, preserving its integrity is important to save the sphincter functions (Figure 3). The major function of the colon is to absorb water from the formed stools and to harden the stools, while the same process gets continued in the rectum, Apart from the absorption of the water, rectum does function like a reservoir which helps in regularising bowel habits of an individual. 

Human Gastrointestinal Tract and Rectum anatomy

Blood supply to descending colon, sigmoid colon, rectum and Autonomic Nervous System controlling Rectum and Bladder Sphincter mechanism 

Mesorectal node, fat and fascia determining plane of dissection 

Etiology

Most cases of rectal cancer are sporadic (70%), with an average age at diagnosis after 50 years old. The remaining 30% are due to the genetic cause (10% due to true inheritance pattern and patients are younger than 50 years of age and the remaining 20% of rectal cancer is seen as familial clustering syndrome. Approximately 5% of all CRC cancers are attributed to familial adenomatous polyposis (FAP) and Lynch syndrome (hereditary non-polyposis colorectal cancer [HNPCC]), the most common named cancer like FAP, Lynch syndrome, Gardner syndrome, Turcot syndrome, Peutz – Jeghers syndrome, Juvenile polyposis syndrome occur due to genetic defect in genes involved in DNA repair genes. Patients carrying these gene defects can have many pre-cancerous polyps in colon which in turn ends up in malignancy and also are predisposed to develop malignancy in multiple sites gastrointestinal tract, hepato-pancreatic-biliary systems, breast and genito-urinary systems as well.

Environmental factors such as diet, reduced physical activity and lifestyle associations for rectal cancer exist. Risk factors such as obesity, red/processed meat intake, tobacco in the form smoking, vaping, chewing tobacco products, alcohol, androgen deprivation therapy has increased risk of rectal cancer. On the other hand, large population studies have found physical activity, diet (fruits and vegetables, fiber, fish), vitamin supplements (folate, folic acid, pyridoxine B6, calcium, vitamin D, magnesium), garlic and coffee, drugs (aspirin, non-steroidal anti-inflammatory drugs [NSAIDs]), hormonal replacement therapy in postmenopausal women, statins for hypercholesterolemia patients have protective factors for rectal cancer. A history of radiation therapy for prostate cancer is another risk factor of rectal cancer. Patients suffering from Inflammatory bowel disease (more commonly ulcerative colitis (UC) than Crohn disease) with rectal involvement increases cancer risk. 

Pathophysiology

The transformation of normal rectal epithelium to a precancerous lesion (adenomas) and ultimately to invasive carcinoma requires an accumulation of genetic mutations either acquired due to various causes mentioned above and/or germline (inherited). Basically, there is a clonal mutation that gives a cell survival-immortality advantage and allows for the development of more mutations providing for cancerous proliferation, invasion and metastasis. There are three major molecular pathways linked to rectal cancer. These are chromosomal instability, mismatch repair, and hypermethylation pathways which can be detected with the mutation analysis tests done with tissue and blood sample. If mutation is detected, then those patients would benefit from initiating immunotherapy. Rectal cancer usually begins with a polyp which typically acquire dysplastic changes over a 10 to 15 year period, leading to invasive carcinoma development (Figure 4). So, early detection and removal of polyps surgically or through colonoscopy, can reduce the incidence of colon and rectal cancer.

Adenoma-Carcinoma Sequence 

Clinical Features and Investigations 

Patients suffering from rectal cancer might have following symptoms.

• Rectal bleeding is the most common presentations of rectal cancer. Hematochezia (passage of red colour blood) and change in bowel habit are more common in rectal cancers.
• Symptoms like change in bowel habits and diminished stool quantity, pain and urgency of passing blood mixed mucus and stools (tenesmus), and constipation.
• In later stages of the disease, other symptoms such as incomplete stool evacuation, pelvic and rectal pain or obstructive symptoms like obstipation (block in passage of flatus and stools) might present.
• In undiagnosed individuals, it can present as an emergency condition where in patient might have obstruction and peritonitis due to perforation.
• Patients diagnosed through routine cancer screening are frequently at an earlier stage compared to the advanced disease seen in incidental surgical findings.
• Sometimes patients can present with haemorrhoids (piles) due to tumour infiltration and resultant engorgement of veins and multiple fistula sites in the perianal area.
• Patients suffering from metastatic rectal cancer may present with clinical symptoms referable to their metastatic sites like liver, lungs and bone.

Patients having any of these symptoms need to approach a Medical, Radiation or a Surgical Oncologist who would evaluate based on the guidelines. Initial investigations would comprise of routine laboratory workups with complete blood count (CBC), iron panel, renal function tests, liver function and coagulation tests. Pre-operative Serum Carcinoembryonic Antigen (CEA) is indicated on all newly diagnosed cases, to assess normalization after surgical resection and for the serial monitoring on follow-ups. This is followed by diagnostic colonoscopy and biopsy to detect the site of the lesion and the distance from the anal verge so as to confirm whether it is high, mid or low rectal cancer. This further helps in the decision making of the type surgery to be offered to the patients.

Baseline CT of the chest, abdomen, and pelvis with intravenous (IV) and oral contrast or PET-CT Scan is the preferred staging imaging study to assess local, regional and distant spread. Contrast MRI pelvis helps to assess the tumour stage in the rectum and is considered better assessment than Contrast enhanced CT scan of the pelvis to assess the tumour stage, mesorectal fat/fascia and mesorectal nodes. This assessment is important as the presence of the disease in the mesorectal fat/fascia and mesorectal nodes necessitates pre-operative chemoradiation and followed by surgery. 

Screening

Breast Cancer, Cervical Cancer, Colorectal Cancer, Lung and Prostate Cancers are the five cancers which can be detected early with the screening tests. Early detection of these cancers can help in achieving cure and also identify individuals who needs close monitoring of disease progression especially the ones with family/genetic history of colorectal cancer or individuals with familial clustering syndromes prone to develop colorectal cancers. As colorectal cancer usually does not show any symptoms until the disease has advanced, it is important for people get colorectal cancer screening done at the age of 45 years and/or undergo screening earlier if they have any of the following risk factors and for colorectal cancer as per American College Of Surgeons recommendation and National Comprehensive Cancer Network (NCCN) guidelines,

• A personal history of colorectal cancer or adenomatous polyps.
• A strong family history of colorectal cancer or polyps, such as cancer or polyps in a first-degree relative younger than 60 or in 2 first-degree relatives of any age. A first-degree relative is defined as a parent, sibling, or child.
• A personal history of chronic inflammatory bowel disease (IBD) like Crohns disease or Ulcerative colitis.
• A family history of any hereditary colorectal cancer syndrome, mentioned in the etiology section. 

The following tests detect both polyps and cancer:

• Flexible sigmoidoscopy every 5 years, or every 10 years with Fecal Occult Blood Test (FOBT) and Fecal Immunochemical Test (FIT) every year.
• Colonoscopy, every 10 years or Double Contrast Barium Enema, every 5 years.
• CT colonography, as often as your doctor recommends.

Following tests are primarily used to detect cancer:

• Guaiac-based Fecal Occult Blood Test (FOBT) or Fecal Immunochemical Test (FIT) every year.
• Stool DNA test, as your doctor recommends (not frequently done in India).

Treatment

Treatment of Rectal cancer is based upon the stage and whether there are any obstruction symptoms due to the growth forming a plug and occludes the passage of stools. Based on these factors, Surgical Oncologist, Medical Oncologist and Radiation Oncologist takes a collective decision on the course of the treatment of Rectal cancer.

1. If a patient presents in the very early stage, with no mesorectal nodal spread or involvement of mesorectal fascia and rectal cancer involving only the muscularis layer of rectal wall, surgery is performed and then based on the histopathology report/IHC/mutation analysis reports, patients will receive chemotherapy/radiation/immunotherapy.
2. If the patient presents with mesorectal nodal spread and mesorectal fascia involvement beyond the muscularis layers of the rectum, then patient will receive total neoadjuvant therapy of chemoradiation and/or immunotherapy and followed by surgery.
3. If a patient presents with above features and solitary liver metastasis or liver metastasis involving 2 or 3 segments of the liver, cure can be attempted based on the above treatment regimen after consulting with the institutional tumour board. Colorectal cancer is the only cancer with this particular subset, even though its considered stage 4, can be still attempted for cure. Most of the liver metastasis disappears after the end of the neoadjuvant and/or immunotherapy treatment, if not, simultaneous surgical resection of liver mets and rectal cancer can be done or combined with interventional radiology techniques for the liver mets.
4. Patients with multiple and diffuse liver and lung metastasis would receive palliative chemotherapy.
5. If a rectal cancer patient presents with obstructive symptoms and multiple perianal fistula, then to relieve obstruction, either temporary diversion ileostomy or colostomy is done to facilitate passage of the stools and once the patient recovers, chemoradiation and/or immunotherapy is given and then definitive surgery is performed to excise the rectal cancer.

Surgeries in rectal cancer depends on the site of cancer whether it is proximal, mid or distal third part of rectum. For the cancers in the proximal and middle third of rectum, primary resection of the mesorectal fascia encompassing the node and tumour is done along with the nodes in the inferior mesenteric artery followed by establishing the continuity of the rectum with descending colon is called as anterior resection (which can be low and ultra-low anterior resection or sphincter preserving resection depending on the site of the final anastomosis to the level of the pelvic diaphragm). But in certain cases where the tumor is in lower rectum and involving anal canal or less than 4 cms from the anal verge, those patients would require abdominal perineal resection of the lesion and will end up with permanent colostomy. This is because, resection of the cancer requires a margin and in rectal cancer, distal free margin should be atleast 2 cms and proximal margin should be more than 5 cms (Figure 5). Rectal cancers at lower third and the ones involving anal canal, achieving distal 2 cms would be difficult and sometimes might compromise or interfere in sphincter function. Thus, leading to frequent fecal soilage and poor quality of life.

Distant margin determining type of surgery performed

To perform these surgeries, it can be done as an open surgery, laparoscopic and robotic surgery. Currently, robotic approach has gained more prominence, as it has 12x magnification with 3D visualisation and 7 degree of freedom movement of the instrument helps one to perform the precise and minimal blood loss during the surgery while compared to the open and laparoscopic surgeries especially when the surgery is to be performed in narrow pelvis. Robotic surgeries are performed by the surgeon using robot as a medium ( Figure 6). Due to its 12x magnification with 3D visualisation, the autonomic nerves are clearly seen and can be easily safeguarded while performing dissection close to the inferior mesentery artery (Figure 7 showing autonomic nerves seen clearly with robotic 12 x magnification and 3D visualisation facility) and in pelvis where rectum is in close proximity with urinary bladder, prostate gland in males and uterus and vagina in females, thereby maintain bowel and bladder sphincter functions. Open surgery is currently practised when there are dense adhesions secondary due to chemoradiation. Apart from these, surgeons can provide chemoport insertions for vascular access, inorder to avoid multiple venous cannulations for chemotherapy purposes.

Stoma (ileostomy/colostomy) care

Generally ileostomy or colostomy created for the temporary diversion for the anterior resection procedure is reversed once the adjuvant therapy is completed. But until then, the stoma is really safe and allows the individual to perform their routine activities like cooking, desk job and attend meetings. There are many myths and stigma attached to the stoma like emitting odour, hampering ones routine activities but these are all not true. It is safe, does not emit any odour but requires to empty the contents once in 3 to 4 hours. Currently, the stoma bags comes with the belt which hitches the bag close to the body plate (unlike the earlier ones) and does not disconnect during any activity. Patients with the stoma can do routine physical activities like walking, jogging, cycling and also wear regular clothes worn prior to surgery.

I have covered the rectal cancer topic briefly and I hope this basic information is sufficient to guide you on rectal cancer, you can approach me if there are any further queries. 

Thank you for patiently going through the article!

Also read:
 

• Decoding Breast Cancer
• Decoding Cancer