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CARCINOMA OF THE COLON

P B Desai
Cons. Cancer Surgeon, Bombay Hospital, Breach Candy Hospital; Prof. Emeritus,Tata Memorial Hospital.

INTRODUCTION

Cancer of the colon is not a very common disease in our country and the incidence is much lower than in the Western world. This is primarily due to predominance of vegetarian dietary habits which has a greater fiber content, less cholesterol, less animal fat as obtains in a predominantly non-vegetarian diet.

Colon cancer is now the second commonest cancer in men and ranks third in frequency in women in the western countries. The incidence of colon cancer according to cancer registry data varies in different parts of the world e.g. in the USA (Connecticut) registry indicating incidence of 35.8/100,000 population. In many developing countries the incidence is less than 10/100,000. In India the estimated incidence rate of colon cancer is documented at 7/1,00,000.

Aetiology

Environmental factors also play a vital role in the causation of colon cancer. A classic example is a change in dietetic habits when people migrate to other countries. In Japan, the incidence of colorectal cancer is low viz 6 to 8/100,000. This incidence increases 2 1/2 times when the Japanese migrate to Hawai (USA) with change in their dietetic habits. Dietary habits have been blamed for development of adenomas of the colorectal region which often acts as a precursor to the development of a polyp which undergoes hyperplasia and subsequent - carcinoma. The polyp-hyperplasia - cancer chain has been well established in the pathogenesis of 2 colonic carcinoma.

Though the link between type of diet and colon cancer appears strong the data cannot be said to be foolproof as conflicting reports do appear. There is of course, a strong suggestion that increased fat intake is conducive to colon cancers.

Colonic cancer is known to have a significant genetic background and families with a very high incidence of colonic cancers are documented in literature in most parts of the world. The classical hereditary disease in the colon is the well-known FAP - familial adenomatous poplyposis-syndrome which carries a high risk for developing colonic cancer. All patients afflicted with FAP will ultimately develop colon cancer unless surgical intevention acts as a prophylaxis.

There are other syndromes associated with colonic cancers and the second one in order of importance is the HNPCC (hereditary non-polyposis colon cancer) which as mentioned above, runs in well documented families, often in siblings.

Progress in genetics will slowly unravel the genetic changes - successive loss of chromosomes - responsible for the development of colonic cancer. Progress in molecular biology has allowed understanding of the characteristics of genetic changes responsible for this multi-step process and in the decades ahead colonic cancer may become a preventable disease.

Symptomatology

The commonest symptom complex is increasing weakness, a drop of Hb (consequent to faecal blood loss), pallor, tiredness and intermittent colicky or dull abdominal pain. These symptoms are the result of either bleeding or colonic obstruction due to growth. Any unexplained anaemia in a young adult - or at any age - calls for a thorough investigation of the GI tract by all modern available technology like endoscopy, ultrasound, CT scan, not forgetting the basic stool examination for occult blood.

Histologic diagnosis

Diagnosis of an established cancer of the colon is not difficult, given the endoscopic surveillance of the whole colon. It is a wise policy to screen the siblings of a patient proven to have a colonic carcinoma by careful clinical history, stool examination, endoscopy and imaging if so warranted.

Polyps or adenomas may be found in high risk individuals and should be carefully studied by an experienced histopathologist after endoscopic removal or biopsy.

Staging

The usual staging is based on Duke's classification with disease localised to mucosa (A), spread into the submucosa (B) and on to the serosa (C) with lymphnode metastasis. Mapping the total profile of the disease (including a good clinical examination) is imperative in planning appropriate treatment strategies.

Clinical examination

In an era of burgeoning technology clinical approach often takes a back seat. This is detrimental to patients interests; for example, no technology can be a substitute for a good clinical examination which can palpate infiltration of the Pouch of Douglas on per rectal examination or a node in the supraclavicular fossa which indicates disseminated disease. Presence of ascites, palpable liver, splenomegaly, presence of umbilical nodules or omental masses will often convey an advanced state of the disease. Presence of anaemia, extreme pallor will indicate a bleeding cancer or a locally advanced disease.

INVESTIGATIONS

Apart from routine blood, urine, stool examination, a baseline CEA estimation is of importance, particularly as nearly 60% of colon cancer will show a rise in the CEA. This will drop to normal after removal of the tumour and will act as a good index to monitor the patient in the follow up period. A rising CEA during the follow up period should arouse suspicion of recurrence of disease at the local or distant site.

Total proteins and their fractions, liver chemistry, chest X-ray, study of cardiopulmonary, vascular and metabolic state should be carefully undertaken pre-operatively to bring the patient to a safe level for surgical intervention.

Endoscopy (S. scopy, colono-scopy) is the next important step and the objective is to study the whole colon upto the caecum. Apart from determining the histology of a given lesion, the state of the rest of the colon, mucosal polyps, adenomas etc. should be carefully recorded and if indicated such polyps and adenomas are best excised and studied histopathologically.

Imaging techniques are useful in indicating the extent of the primary disease, its infiltration into the mesentery, surrounding structures and involvement of the liver or other organ. A standard ultrasound and CT scan are well worthwhile despite the cost factor as findings may warrant that radical surgery may not be fruitful. Particularly if there is no obstruction or bleeding. A palliative by-pass even in an advanced setting is indicated to obviate obstructive symptoms.

Spread of colonic cancer

The pattern of spread is generally predictable from mucosa to submucosa to muscle and serous layers to pericolic tissues - nodal spread to pericolic, mesenteric nodes with the disease ultimately setting into the liver.

Contiguous spread to adjacent structures viz : abdominal wall, psoas muscle, duodenum, head pancreas are seen in late cases. This does not necessarily indicate non-resectability as occasionally in selected cases major excision of contiguous organs (like duodenum, head pancreas - colo - whipple procedure) are sometimes indicated in a selected case and may result in long term survival.

Diffuse peritoneal dissemination will result in miliary seedlings and ascites; liver metastasis, neck node metastasis and spread to the skeleton, lungs and brain may occur in terminal stages precluding even palliative resection.

Surgical approach - standard care

For a standard resectable non-metastatic colon cancer, the principles of surgery have remained unchanged. A right, transverse or left hemicolectomy encompassing the lymphdrainage area is standard surgical care.

Colonic resections with adjacent structures and organs Appropriately indicated aggressive surgery where the disease can be encompassed, often gives satisfactory results and gives lasting palliation.

Excision of the lesion with part of abdominal wall, psoas muscle, nephrectomy and even a whipples procedure (Pancreatico duodenectomy) along with colonic resection have indications. The surgery should be able to remove all gross disease, and the experience of the surgeon should be commensurate with the procedure and the patients general condition should be such so as to withstand the procedure. As mentioned earlier, long lasting palliation and occasional cures have resulted after this aggressive surgical intervention in appropriately selected cases.

Resection of liver or lung metastasis

Localised solitary metastasis appearing 2 or 3 years after primary surgery are best tackled with conservative resectional surgery on the liver or the lung.

Adjuvant therapy

Administering chemotherapy in an adjuvant fashion (after surgery) is standard care in colonic cancers when the surgical pathology indicates :

  1. Presence of nodal metastasis
  2. Large tumour size with infiltration of serosa or peri-colic tissues
  3. High grade tumours

All dukes B and C tumours should receive 4 to 6 cycles of 5FU / leucovorin / cisplatin based chemotherapy.

Palliation

When at initial presentation there is dissemination in the liver or to a distant site, chemotherapy is the only treatment that may be feasible. Even in such situation, a surgical bypass or colostomy may be indicated if there is bowel obstruction or excessive bleeding.

When at initial presentation there is dissemination in the liver or to a distant site, chemotherapy is the only treatment that may be feasible. Even in such situation, a surgical bypass or colostomy may be indicated if there is bowel obstruction or excessive bleeding.

In a patient with peritoneal dissemination, ascites, liver metastasis etc. often the best treatment could be good symptomatic care.

Radiotherapy has a limited role in cancer of the colon. In non resectable colonic cancers, after a surgical bypass has been achieved, palliative radiotherapy could be given to the primary lesion for pain relief.

Radiotherapy can also be considered for painful bony metastasis or abdominal masses.

SUMMARY

Cancer of the colon is related to diet, genetics and environment. The pathogenesis of adenoma-polyp-hyperplasia-carcinoma is well established.

Progress in genetics may one day be able to prevent colon cancer. Any patient with weakness, anaemia, abdominal discomfort should be investigated for excluding a colonic carcinoma by endoscopy, barium studies, imaging by ultra sound, CT scan etc. Surgery remains the treatment of choice and a complimentary treatment approach becomes necessary in most cases. High cure rates can be achieved in early cases or good palliation can be achieved in advanced cancers by appropriate palliative surgery, chemotherapy and radiotherapy. Cancer of the colon, when diagnosed early and treated effectively has a high cure rate of nearly 70% survival at 10 years.

REFERENCES

  1. Cancer - Principles and practice of oncology. 5th edition. Denta, Hellman, Rosenberg.
  2. Hospital based cancer registry data. Tata Memorial Hospital - 1977.
  3. Seminars in surgical oncology. Colo Rectum. 1998.