Colorectal cancer

Dr Daleen Geldenhuys gives us an explanatory rundown on colorectal cancer and the treatment thereof.

You can listen to this article below, or by using your favourite podcast player at pod.link/oncologybuddies

Incidence

Colorectal cancer (CRC) is a frequent cancer worldwide and can be prevented by early detection and removal of precancerous lesions.

It’s the third most common malignancy and the second most deadly cancer worldwide. There is an estimated 1.9 million incidence cases and 0.9 million deaths worldwide every year. The incidence of CRC is higher in highly developed countries, and it’s increasing in middle- and low-income countries due to westernisation. Moreover, a rising incidence of early-onset CRC is also emerging. 

Symptoms

Presenting symptoms include a change of bowel habits, abdominal discomfort, and, less frequently, visible blood in the stool.

Diagnosis

The diagnosis is usually made by colonoscopy and biopsy of the lesion/s at the time.

Workup before surgery usually includes radiographic imaging, such as a CT scan, but may also include an MRI when rectal lesions need to be better visualised or when liver metastases may be present.

Tumour markers are only useful in the monitoring process and may not be elevated at all despite a positive diagnosis. The two markers used are CEA and CA 19-9.

Genetic predisposition

A family history of colorectal and other extracolonic cancers (going back three generations, if possible, but at least first- and second-degree relatives) should be sought, as the patient’s siblings, children and even parents may be at risk. 

Pathology

After surgery, the pathologist will comment on microsatellite instability and the possible presence of multiple polyps in the surrounding colon to alert the patient to a possible familial risk. 

Left-sided cancers have a better prognosis than right-sided cancers. The lymph node involvement is important for staging purposes. Certain mutations can be commented on to individualised therapy.

Treatment

Surgical resection is vital to eradicate the disease. It may involve a temporary diverting colostomy (stoma bag) if the rectum is involved, or the tumour may be completely obstructive, needing neoadjuvant chemotherapy first. This may be if there is liver involvement or local infiltration of other organs such as the bladder.

Neoadjuvant chemotherapy may be indicated and useful to reduce the risk of micro metastases, reducing the primary tumour to facilitate surgical resection and better compliance with systemic therapy when it’s delivered preoperatively. It’s also indicated when dealing with advanced metastatic disease and control of the metastatic lesions may be more important than removing the primary CRC tumour.

Observational studies suggest that perioperative chemotherapy is safe and doesn’t worsen post-operative complications. Some randomised studies demonstrate a consistent benefit with perioperative chemotherapy such as reduced rates of disease recurrence. It also gives an idea of tumour sensitivity and complete pathological response at the time of surgery confers a lower risk for recurrence. However, these decisions should be made in the best interest of the individual patient.

Post-operative radiation isn’t usually considered a routine component of care for completely resected colon cancer. This contrasts with patients with rectal cancer where radiation forms a vital part in the treatment either before or after surgery. Total neoadjuvant therapy is preferred where the patient will receive chemotherapy as well as chemo-radiation combination therapy to improve local and systemic control. 

Adjuvant chemotherapy is indicated if no treatment was given prior to surgery and the staging is locally advanced. Usually Stage 2b and higher will need chemotherapy but should be individualised depending on the individual patient. 

Stage 4 disease

Approximately 20 to 25% of newly diagnosed colon cancers are metastatic at presentation (synchronous metastasis). Others may develop metastatic disease after potentially curative treatment of localised disease. 

The most common distant metastatic sites are the liver, lungs, lymph nodes, and peritoneum. Depending on the disease burden and sites, curative resections may be performed.

With major advances in systemic chemotherapy, immunotherapy and targeted agents, the median survival has increased significantly for CRC.

Patients with deficient mismatch repair (dMMR) metastatic colon cancer respond to immunotherapy.

Surveillance

Post-treatment surveillance is important to detect early recurrence. This includes regular physical examination, colonoscopy, blood tests and scans when indicated.

Never ignore constant tiredness (blood loss), visual rectal bleeding, weight loss and a change in bowel habits. The disease can be successfully treated and even prevented.

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