COLORECTAL CANCER
المحاضر: الدكتور خلدون ذنونكلية طب نينوى- المرحله الرابعة
Objectives
1. To know the features of such serious disease for the sake of early diagnosis.
2. endoscopy and biopsy are essential.
3. Staging of the disease which influence management.
4. Surgery, chemotherapy, and radiotherapy are the mainstay of management.
Introduction
Its incidence is increasing in Iraq .The second most common malignancy & the second leading cause of cancer death in the west .
Occur mainly after 50 y of age .
Etiology
Risk factors : 80% sporadic , 10-15% family history , 5% hereditary non-polyposis colon cancer , 1% familial adenomatous polyposis , 1% inflammatory bowel disease .A-Environmental factors : account for 80% of sporadic colorectal CA 1.Dietary factors : red meat (carcinogenic amines formed during cooking) , saturated animal fat (high faecal bile acids) , risk is decreased by : dietary fiber , fruit & vegetables , calcium which binds & precipitates bile acids , folic acid .
2.Non-dietary risk factors : colorectal adenoma , long standing extensive UC , acromegaly , pelvic radiotherapy , obesity & sedentary life style , alcohol & tobacco (weak association), cholecystectomy, type 11 diabetes.
B-Genetic factors
Due to chromosomal instability and multiple genetic mutations .
10% strong family history of CA colon at an early age .
1% familial adenomatous polyposis – autosomal dominant .
5% hereditary non-polyposis colon cancer :
. Autosomal dominant
. Failure of DNA mismatch repair leads to multiple somatic
mutations throughout the genome.
. Life time risk of colon cancer is 80%
. Mean age of disease onset is 45y
. 2/3 tumor occurs in the proximal colon (sporadic cancer-distal)
. Increase incidence of cancer in endometrium , urinary tract ,
stomach & pancreas
. Genetic testing & colonoscopy every 1-2 years for such families
begin at age 25 year
Pathology
Most tumors arise from benign adenomatous polyp .
More than 65% occur in rectosigmoid , 15% in caecum & ascending colon .
Polypoid (fungating) or annular & constricting .
Spread through bowel wall , rectal cancer may invade pelvic viscera.
Lymphatic invasion is common & through portal and systemic circulation reach the liver and less commonly , the lungs .
Tumor stage at diagnosis determines the prognosis .
Dukes stage A- Tumor limited to mucosa & submucosa (highest
survival) .
B- Cancer involves muscularis & extends into or through
serosa .
C- Regional lymph node involvement
D- Distant metastasis e.g liver , lung (lowest survival) .
Clinical features
Symptoms depend on tumor location .Left colon cancer : fresh rectal bleeding is common & obstruction occur early.
Right colon cancer : present with anaemia from occult bleeding , altered bowel habit , obstruction is late , 2/3 colicky lower abdominal pain, rectal bleeding in 50% , minority develop obstruction or perforation leading to peritonitis , localised abscess or fistula formation .
Rectal cancer : early bleeding , mucus discharge , feeling of incomplete emptying .
10-20% of all patients present with iron deficiency anaemia or weight loss .
sometimes it presents as fever of unknown origin .
Examination : palpable mass , anaemia , hepatomegaly , low rectal tumors are palpable by PR .
Investigations
Colonoscopy is the investigation of choice as it is more sensitive & more specific than barium enema , biopsies can be taken & polyp removed.
CT detects abdominal involvement of the viscera e.g liver , and lymph node involvement i.e stage of tumor , intraoperative U/S can do the same job .
Endoanal U/S or pelvic MRI stages rectal cancer .
CT colography is sensitive non-invasive technique for diagnosis.
Increased CEA : non-specific , of little use in the diagnosis but valuable in follow up after surgical resection to detect recurrence .
Management
A- surgery : removal of the cancer with adequate resection of margins and pericolic lymph nodes , some may need colostomy others need end to end anastomosis .CA near anal verge may need abdomino-perineal resection with colostomy .
solitary hepatic or lung metastasis may be resected .
Post-operative colonoscopy after 6-12 months & periodically there after to detect recurrence or new cancer which occurs in 6% .
B- Adjuvant therapy
2/3 have lymph node or distant spread at presentation & so surgery is not curative .
5-fluorouracil + folinic acid (reduce toxicity) improves survival in patient with Dukes C stage after surgery and is also palliative for patients with metastasis .
Pre-operative radiotherapy is given to patients with large-fixed rectal cancers to down-stage the tumor.
Pelvic radiation for pain and bleeding.
Post-operative radiotherapy to patients with Dukes C & some Dukes B rectal cancers to reduce the risk of recurrence .
Monoclonal antibodies (bevacizumab) alone or with chemotherapy are useful for metastatic disease.
Tumor obstruction can be relieved by endoscopic laser ablation or metal stent.
Secondary prevention & screening
Detect & remove lesions at an early or pre-malignant stage .
Wide spread screening by regular faecal occult blood FOB testing , reduces colorectal cancer mortality by 15-20% & detect cancer early , but it lacks sensitivity&specificity , USA: annual FOB screen after 50y.
Colonoscopy is the gold standard(needs well-trained persons,expensive,risk of the procedure).
Flexible sigmoidoscopy is the alternative option, it reduces overall colorectal cancer mortality by 35% & 70% for rectosigmoid CA. , done in USA every 5 years for those above 50 years of age .
Screening for high-risk patients by molecular genetic analysis : not yet available .
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