Colorectal cancer

COLORECTAL CANCER  

In western countries ,colorectal cancer ranks second to lung cancer in incidence and mortality rates.Adenomas are probably te precursors of most,if not all ,colorectal cancers.Multiple synchronous colonic cancers,i.e two or more carcinomas occurring simultaneously,are found in 5% of patients.Metachronous cancers is a new primary lesion in a patient who has had a previous resection for cancer.The risk of metachronous tumors reaches 25% after 20 years of follow-up.The incidence f colonic cancer appears to be rising,especially cancer of the right side of the colon and of the sigmoid colon.

Invasive cancers that are confined within the wall of the colon (TNM stages I and II) are curable with surgery. If untreated, they spread to regional lymph nodes (stage III), where up to more than 70% are curable by surgery and chemotherapy. Cancer that metastasizes to distant sites (stage IV) is usually not curable, although chemotherapy can modify survival, and in thin cases, surgery and chemotherapy together have seen patients through to a cure. Radiation is used with rectal cancer.

ETIOLOGY

Rectal cancer usually develops over several years, prototypal growing as a precancerous growth called a polyp. Some polyps have the knowledge to turn into cancer and begin to acquire and penetrate the wall of the rectum. 

The actual cause of rectal cancer is unclear.

However, the following are venture factors for nonindustrial rectal cancer: 

Genetics : Family cancer syndrome.

Environmental : Low fibre ,high fat diet.

Inflammatory bowel disease.

Polyposis syndrome.

Personal history of colon polyps or colon cancer.

Precarcinomatous conditions

(a) adenoma.

(b) papiloma.

Family history is a bourgeois in determining the venture of rectal cancer. If a family history of colorectal cancer is present in a first-degree relative (a parent or a sibling), then endoscopy of the colon and rectum should begin 10 years before the geezerhood of the relative's diagnosis or at geezerhood 50 years, whichever comes first.

An ofttimes forgotten venture factor, but perhaps the most important, is the lack of screening for rectal cancer. Routine cancer screening of the colon and rectum is the prizewinning artefact to prevent rectal cancer. 

STAGING OF COLORECTAL CARCINOMA BASED ON DUK's CLASSIFICATION ,WITH SURVIVAL RATES AFTER SURGERY

DUK'S GRADE        SPREAD                                                5 YEAR SURVIVAL

A                        Confined to bowel wall                               90%

B                        Spread through the bowel wall                    70%

C                        Spread to lymph nodes                             30%

Stage D was added to Duk's classification later,based on clinical rather than pathological evidence.

Stage D implies distant metastases.

COMPLICATIONS

These include obstruction, perforation (direct perforation of the tumor ) ,obstruction ,perfortion into an adjacent organ with development of a fistula.e.g colovesical , and symptoms relating to direct extension.

PROGNOSIS

This depends on the degree of differentiation of the tumor ,the completeness of excision and the degree of spread.Examination of the resection margins ( proximal.distal and circumferential ) to assess completeness of excision is required.The extent of spread through the bowel wall and the presence of lymph node metastases are other major prognostic indicators.The extent of spread is given by the Duk's classification,whih is also related to prognosis.