Cancer of the colon

Symptoms and diagnosis

Large bowel cancers are much more common and chiefly affect the distal large bowel, particularly the rectum and sigmoid colon. Characteristically they occur as fleshy, polypoio growths and tend to spread locally, through the bowel wall to the exterior surface, unlike esophageal tumors which spread up and down. Haema-togenous spread is usually via the portal vein to the liver, though other sites such as bone and lung can be involved. The degree of penetration of the bowel wall and involvement of local lympathics together form the basis of the Dukes staging system which gives an excellent indication of the likely outcome following surgery.

Clinical presentation includes abdominal pain, change in bowel habit, rectal bleeding, weight loss and obstructive symptoms, through the frequency of these features clearly varies with the site of the tumor in the bowel. For example, with rectal carcinomas, change in bowel habit and rectal bleeding are generally present, though obstructive symptoms are uncommon. There is usually no palpable abdominal mass though a rectal examination generally reveals the correct diagnosis without difficulty. On the other hand, in tumouts of the ascending colon, abdominal pain with a palpable mass are fairly consistent features, while rectal bleeding, constipation or diarrhea are less common. Careful abdominal and rectal examination of patients with any of these symptoms is mandatory, and early referral should be considered. Sigmoioscopy, colonoscopy and barium enema studies usually give a reliable pre-operative diagnosis, though CT scanning may give additional information and may also confirm inoperability without subjecting the patient to an unnecessary laparotomy. Although there is no reliable plasma market for these tumor, the serum CEA (carcinoembryonic antigen) level is often elevated, and can be useful either at diagnosis or as a means of predicting relapse following treatment, even before any symptoms supervenue.

Management

These tumors are the province of the surgeon. Wide excision is undoubtedly the treatment of choice and the operative details of course depend on the site of the lesion. It is generally possible to perform either a left or right hemicolectomy with end-to-end anastomosis for sphincter preservation. Low rectal tumors may, however, require abdominoperineal resection with a permanent colostomy. Recent surgical advances have permitted sphincter preservation for an increasing number of patients with rectal tumors. In clearly inoperable tumors, local irradiation should be considered as they are partly responsive, and treatment can often produce an improvement in symptoms. Bowel diversion by colostomy can be particularly helpful in such cases, allowing a reasonably high dose of radiotherapy to be given, with a correspondingly more durable remission, Though surgical mortality is now low, complications are still quite common, and include anastomotic leak, pelvic abscess, abdominal fistulae and post-operative wound sepsis. Local recurrence remains a major problem, but it now seem clear that this may be reduced by the routine use of post-operative radiotherapy.

Most patients find life with a colostomy tolerable, though care must be taken to teach correct maintenance techniques from the outset. Patients should be measured that modern colostomy bags are extremely reliable and do not burst or allow escape of offensive gas. Is it important to avoid local spillage of bowel contents onto the skin as this causes subsequent excoriation. Most large hospitals have stoma nurses to help with support, and patients should generally be able to take over their own care without undue difficulty.

Apart from its palliative value, there is  increasing evidence that radiotherapy could become an important part of routine management of rectal cancers. Two large American multicenter studies comparing surgery alone with surgery plus radiotherapy, have shown survival benefit, particularly in the more advanced tumors. This approach has not yet been widely accepted in the UK. In cancers of the anus, radiotherapy has also begun to compete with surgical excision, since surgical removal almost invariably means permanent sphincter loss, while radiotherapy does not usually interfere with normal sphincteric function. This is another site where interstitial radiation therapy techniques have been developed. One further exciting advance, still not fully established, is the use of concomitant radiotherapy with chemotherapy, which may result in remarkable local control even in bulky tumors.

Chemotherapy alone is not very successful in the management of large bowel tumors, though responses are seen with 5-fluorouracitegafur, Doxorubicin and few newer drugs plus the nitrosourea group. However, chemotherapy for recurrent diseas does not appear to improve survival substantially. Although response rates are only of the order of 25%, the drugs may be more useful given as adjuvant therapy after primary bowel resection, particularly since 5- fluorouracil and other drugs are so well tolerated. One randomized trial of peri-operative intraportal 5- fluorouracil has shown improved survival compared to control patients undergoing surgery alone. Results from several large studies investigating this technique are awaited.

Overall prognosis depends largely on the stage of the tumor and early stage carcinomas confined to the mucosa and sub-mucosa have an excellent five year survival rate. Careful follow-up is essential for all patients since some recurrences are essentially local in nature, and further surgery may still be curative.