Colorectal cancer treatment side effects that nobody talks about

When patients with colorectal cancer are undergoing or complete cancer treatment, it is common for them to experience side effects such as fatigue, nausea, numbness in their hands and feet, and changes to their skin.

However, one lesser discussed, commonly occurring side effect are changes in bowel habits which can persist long after treatment ends. Understandably many patients find it embarrassing to discuss how this can significantly impact their daily life, work and social activities, as well as cause distress and feelings of isolation.        

Clin Asst Prof Evelyn Wong, Consultant, Division of Medical Oncology, NCCS, offers practical tips for how to manage changes in bowel habits after treatment. 

To help with patients and caregivers understand ways to deal with this, Clinical Assistant Professor Evelyn Wong, Consultant, Division of Medical Oncology, National Cancer Centre Singapore (NCCS), offers practical tips.

A common and treatable cancer

Colorectal cancer is a disease that develops in the colon (large intestine) or rectum, the final part of the digestive tract. According to the Singapore Cancer Registry Annual Report 2023, colorectal cancer is the second most common cancer in Singapore.

Treatment typically involves surgery to remove the tumour, and depending on its location, size, and stage of the cancer, this may be combined with chemotherapy and radiotherapy. As colorectal cancer is now highly treatable when detected early, issues, including managing long-term side effects such as bowel function, are becoming increasingly important for colorectal cancer survivors.

Why bowel changes occur after treatment

Changes to digestion and toileting occur during and after colorectal cancer treatment, as it affects the bowel’s flow, storage capacity and the nerves and muscles that help to control bowel movements.

For example, surgery which removes part of colon or rectum, may reduce the bowel’s capacity to store stool, while radiotherapy can cause inflammation of the bowel lining and chemotherapy can affect the gut lining and the balance of gut bacteria.

Changes in bowel habits are common post-treatment but often improve as the body heals. It is important for patients to seek medical help early. (Credit: iStock.com/Chainarong Prasertthai)

“Changes in bowel habits are common, especially in the first weeks to months post treatment,” said Asst Prof Wong. “This may include more frequent bowel movements, needing to rush to the toilet, diarrhoea, constipation, incontinence, feeling of incomplete emptying, bloating, cramps and excessive wind. Patients with a stoma (a surgical opening on the stomach that connects the digestive system to the outside of the body to allow waste to be collected in an external pouch) may experience high output, gas, skin irritation, or difficulties with the stoma fitting.”

While these symptoms can be distressing, they are often treatable and tend to improve as the body heals. It is important for patients to inform their doctor early to seek help rather than face these challenges alone. 

Bowel dysfunction is more common than you think

“Bowel dysfunction after colorectal cancer treatment is more common than many patients realise. However, patients often feel embarrassed or assume this is something they must accept, and they avoid discussing it since it is not life-threatening. Changes to your bowel habits should not be dismissed or endured in silence, and you should speak to your doctor as support and treatment options are available to help patients regain confidence and quality of life,” said Asst Prof Wong.

Ms Felicia Lee underwent preventive colon removal surgery at 15 and returned to school within two weeks. She encourages other patients that symptoms will improve over time. (Credit: Ms Felicia Lee)

“The duration of the side effects varies among patients and the type of treatment received. Many symptoms improve over time, particularly in the first year,” shared Ms Felicia Lee, 42, homemaker and Familial Adenomatous Polyposis (FAP) patient.

"I was diagnosed with FAP when I was 12. During a routine check at 15, the doctor discovered a large polyp along with several other polyps in my colon. I was advised to undergo surgery to remove my entire colon as a preventive measure to reduce my future cancer risk. Later, a biopsy revealed that the large polyp was indeed cancerous,” said Ms Lee.

Ms Lee had the surgery at 15 and returned to school just two weeks later. She used a stoma bag for three months before undergoing a second surgery to reconnect her small intestine to her rectum.

FAP is a hereditary cancer syndrome that increases the risk of colon cancer to nearly 100%. Individuals with FAP are typically recommended to undergo preventive colon removal surgery.

Colorectal cancer survivor Ms Joelle Kong returned to coaching sailing after surgery by packing spare clothes, adjusting her diet, and getting adequate rest to manage side effects. (Credit: Ms Joelle Kong)

“For the first few months, I went to the toilet 18 times a day! But my body adapted, and life returned to normal after a year. Now, I simply watch my diet, avoid spicy food, and stay more conscious of my health,” said Ms Joelle Kong, 34.

A freelance sailing coach and colorectal cancer survivor, Ms Kong also had side-effects but developed ways to manage them so she could continue with her regular routine.

“I had two-thirds of my colon removed and experienced side effects including fatigue, lactose intolerance and occasional loose stools. Since I was determined to continue coaching after recovering from surgery, I made sure to always pack an extra set of clothes, watch my diet and get sufficient rest daily.”

Managing bowel dysfunction

Frequent or unpredictable bowel movements can affect patients’ confidence, willingness to socialise and ability to return to work. The good news is that they can often be managed with appropriate support, medications and advice, such as:

• For loose stools or diarrhoea: Start anti-diarrhoeal medication early, as prescribed, and use oral rehydration agents if stools are frequent. Stool-bulking agents can also help to thicken stool and reduce urgency. Avoid food and drink that can make diarrhoea worse, such as caffeine, alcohol, oily or spicy foods, and dairy products.
• For urgency or leakage: Speak to your care team about pelvic floor physiotherapy, bowel retraining, and timed toileting routines. Use barrier creams and gentle wipes to protect skin from soreness.
• For constipation: Ensure sufficient fluid intake and do light, low-impact exercises. Adjust fibre intake as advised by your care team and use prescribed laxatives or stool softeners to avoid alternating between constipation and diarrhoea. 
• For bloating and wind: Eat smaller, frequent meals and slowly reintroduce high-fibre foods. Find out which foods make your symptoms worse, such as onions, beans, certain vegetables, or fizzy drinks.
• For stoma patients: Work with your stoma care nurse for appliance fitting, leakage management, skin care and dehydration.

“There is no one-size-fits-all approach. Keeping a simple record of bowel patterns, frequency, and triggers can help your care team provide personalised advice,” advised Asst Prof Wong.