Colorectal cancer is the third most common Cancer in the Western world. In India, its incidence is increasing especially among patients in Kerala. In the west, the probability of a person to suffer from Colon or Rectal cancer is 6% in their lifetime.
Worldwide, over a million patients are diagnosed with colorectal cancer with over 500,000 associated deaths reported. Environmental factors, especially the dietary ones have played a role in the rise of cancer rates.
Colon Cancer and Genetics
Cancer cells grow in an uncontrolled manner and have the ability to invade surrounding structures and spread to far off organs via the blood stream or lymph vessels (metastasis). Alteration in genes result in the cells transforming – and this is called the Adenoma-Carcinoma cascade.
There are two well defined genetic pathways leading to the development of colorectal cancer. The chromosomal instability within (CIN) pathway is the result of an accumulation of inactivated tumor suppressor genes and overactive proto-oncogenes. Tumors developing along this pathway are characterized by mutations of the APC, p53 and K-ras genes. Microsatellite instability pathway is the other well described genetic cascade implicated in the development of colorectal cancer.
Risk factors for colon and rectal cancer
The development of colorectal cancer in words interplay between genetic and environmental influences. The most easily identifiable risk factors include age greater than 50, a personal or family history of colorectal cancer or adenoma, and a personal history of long-standing inflammatory bowel disease. Colon cancer that develops in individuals without hereditary links are referred to as sporadic and account for up to 75% of all colorectal cancers. Potential genetic influence is identified in the remaining 25% of patients including family history, Lynch syndrome and FAP (Familial Adenomatous polyposis).
Age is the most common risk factor. The incidence of colorectal Cancer increases from the 4th to the 8th decade of life. Personal history of colorectal polyps is also a significant risk factor.
Inflammatory bowel disease
Patients with inflammatory bowel disease (IBD) are at a significantly increased risk of developing colorectal cancer. The risk is directly proportional to the extent and duration of disease.
Colorectal cancer screening
The goals of screening asymptomatic patients are to identify and remove polyps which may be precursors of malignancy. Colonoscopy also helps to identify early malignancies. A large study confirmed that colonoscopic polypectomy reduces colon cancer mortality.
In India, the general population is not considered to be at a high risk, the screening programme should be targeted towards individuals who are at a greater risk of developing Colon and rectal cancer. High risk individuals include those with personal history of adenomas are cancers, family history of adenocarcinoma or genetic syndromes, or predisposing medical conditions such as inflammatory bowel disease .
There are well established screening protocols for high risk individuals which should be adhered to.
Staging of colon and rectal cancer
Colorectal cancer is related to the stage of disease at diagnosis and tumour biology. Another important factor is whether the tumour has invaded the margins of surgical resection. These details can only be ascertained after the surgical procedure and are reported by a qualified gastrointestinal pathologist. The Tumour, Node and Metastasis (TNM) Staging system of the AJCC is the standard colorectal cancer Staging system.
Treatment of Primary Colon and Rectal cancer
Surgery is the mainstay of therapy for Colon and rectal cancer. Surgery is currently preferred via keyhole or laparoscopic procedure as it is associated with improved postoperative recovery and equivalent tumor clearance compared to open surgery. The common procedures that are carried out for Colon and rectal cancer are Right Hemicolectomy, Left hemicolectomy, Segmental colectomy, Sigmoid colectomy, Anterior resection, Low anterior resection and Abdomino-Perineal resection (APR). These procedures when done via the minimal access route generally facilitate quick recovery following the surgical procedure. Some of those procedures may need either a temporary or a permanent stoma which is managed by a qualified stoma nurse.
Although complications following surgery are infrequent, the surgeon has to keep a close eye on the patient following surgery to look for any danger signs and take remedial measures as early as possible.
Chemotherapy for colorectal cancer
Chemotherapy is administered to patients following detailed examination of the tumor specimen by the pathologist. The oncologist in consultation with the surgeon suggests an appropriate regime which is tailored for each individual patient depending on the extent of the tumor spread and staging.
80% of patients who recur after curative resection of colon and rectal cancer do so within 3 years. Therefore, any post-treatment plan should include regular followup during at least these 3 years . In general serum CEA testing should be performed every 3 to 6 months for 2 years then every 6 months for a total of 5 years after resection of the primary tumor. Chest, abdomen and pelvic CT is recommended annually for 3 years for patients at high risk for recurrence.
Colonoscopy should be performed one year after surgery and then 3 years later and then every 5 years unless findings of specific risk factor dictate more frequent evaluations. Routine cancer follow up and surveillance is typically considered completed after approximately 5 years.
Colonoscopic surveillance however is routinely recommended to continue indefinitely.