colorectal cancer:screening & diagnosis

 

Overview

• Most cancers develop from adenomatous polyps. Screening for colorectal cancer has been shown to reduce mortality by 16%

• The NHS now has a national screening programme offering screening every 2 years to all men and women aged 60 to 69 years. Patients aged over 70 years may request screening

• Eligible patients are sent faecal occult blood (FOB) tests through the post

• Patients with abnormal results are offered a colonoscopy

At colonoscopy, approximately:

• 5 out of 10 patients will have a normal exam

• 4 out of 10 patients will be found to have polyps which may be removed due to their premalignant potential

• 1 out of 10 patients will be found to have cancer

Diagnosis

Essentially the following patients need referral:

• Altered bowel habit for more than six weeks

• New onset of rectal bleeding

• Symptoms of tenesmus

Colonoscopy is the gold standard, provided it is complete and good mucosal visualisation is achieved. Other options

include double contrast barium enema and CT colonography.

Staging

Once a malignant diagnosis is made patients with colonic cancer will be staged using chest / abdomen and pelvic CT.

Patients with rectal cancer will also undergo evaluation of the mesorectum with pelvic MRI scanning.

For examination purposes the Dukes and TNM systems are preferred.

Tumour markers

Carcinoembryonic antigen (CEA) is the main tumour marker in colorectal cancer. Not all tumours secrete this, and it may be raised in conditions such as IBD. However, absolute levels do correlate (roughly) with disease burden and it is once again being used routinely in follow up.

 Dukes Classification

 Gives the extent of spread of colorectal cancer

Dukes A Tumour confined to the bowel but not extending beyond it, without nodal metastasis (95%)

Dukes B Tumour invading bowel wall, but without nodal metastasis (75%)

Dukes C Lymph node metastases (50%)

Dukes D Distant metastases (6%) (25% if resectable)