COLON CARCINOMA: PECULIARITIES IN NIGERIA. A REVIEW.
BY: EROMOSELE BENJAMIN O.
AS AT TIME OF WRITING, 2ND YEAR CLINICAL STUDENT, COLLEGE OF MEDICINE, UNIVERSITY OF IBADAN, IBADAN.
EROMOSELE BENJAMIN OSEIWE
Department of Medicine and Surgery,
College of Medicne,
University of Ibadan,
Typically referred to as a disease of Caucasians, the incidence of colon carcinoma is growing in Nigeria. In this review, factors that may be accounting for this trend are looked at, as well as the peculiarities of the disease in Nigeria and Africa at large.
Colon carcinoma in Nigeria comes with its peculiarities such as, late presentation; such that most cases present at an advanced stage with incurable disease, increasing adoption of ‘Western’ diets and lifestyle; such as, consumption of high fat, low fibre diet, and reduced physical activity, which is suspected to be responsible for the increasing incidence of the disease, and a paucity of polyposis coli syndromes.
The aim of this review is to emphasize;
- that colon carcinoma is not a disease of only Caucasians and that the incidence is even increasing among native Africans
- the peculiarities of this disease among Nigerians in particular and Africans at large
- the pointers to early diagnosis
- preventive measures to this potential epidemic
MATERIALS AND METHODS
The materials used in this review article comes from studies and publications on colorectal carcinoma.
Colon, carcinoma, peculiarities and review.
Colon carcinoma in traditional descriptions, is said to be uncommon among native Africans. Once the 10th most common malignancy in men from the Ibadan cancer registry four decades ago (1960 to 1969), now holds as the fourth most common malignancy . This shows an increasing incidence.
Even with an increasing incidence, reports estimate that about 6 to 25 patients present annually in Nigerian tertiary health care centers[2-9]. This shows that it is still relatively uncommon compared to other westernized societies. Awarness must be put in place to halt this potential ‘outbreak’, considering resource constraint on the part of the government in solving issues such as this in Africa, with Nigeria in particular. This is further complicated by the fact that most Nigerian patients present late with advanced disease, with a significant proportion in comparison to Caucasian cases, being the mucin-producing adenocarcinoma which carries a worse prognosis .
In contrast to other westernized societies, there is a paucity of polyposis coli syndromes among Nigerians  such as Lynch syndrome which confers a hereditary predisposition to colon cancer. In Nigeria only four cases of adenomatous polyposis have been reported in the last thirty five years [11,12,13,14]. The mean age incidence of colon carcinoma in Nigeria is 41 years, with Ibadan as reference , with an incidence rate of 3.4/100,000, the increasing incidence may be attributed to an increasing adoption of westernized lifestyle, increasing life expectancy; due to an increasing access to better health care, since colon carcinoma is sometimes referred to as a disease of aging, among other reasons.
With an increasing incidence of colon carcinoma in Nigeria, the peculiarities of the typical Nigerian picture of colon carcinoma are discussed below
The carcinogenesis of colonic carcinoma among Nigerians is somewhat controversial. The typical adenoma-carcinoma sequence seems unlikely among Nigerians [4,15,18,19]. This is supported by the fact that studies show that it takes fifteen to twenty years for malignant change to occur in an adenoma[9,20], making it unlikely in Nigerians since the age incidence of clinical disease is relatively commoner among the younger age group. The microsatellite instability theory holds true more commonly for hereditary nonpolyposis colorectal carcinoma , which is rare among Africans.
This raises the suggestion that most cases of colon carcinoma in Nigeria occur sporadically, with an adequate environmental influence.
The clinical presentation depends on the site affected. The most common site in Nigeria appears to be the caecum , which may present as an abdominal mass . In right sided disease, presentation is usually that of an iron deficiency anemia due to chronic blood loss. In left sided disease, the features are those of obstruction such as change in bowel habit, chronic constipation; since the stenosing variant of colon carcinoma seems more common here . In the transverse colon, the features here are determined by the proximity to either the right or left side. If closer to the right, features are similar to right sided disease and if close to the left; features are similar to those of left sided disease. Bleeding per rectum, hemorrhoids due to obstruction of the superior rectal vein  and tenesmus may also be seen. It is also noteworthy that most patients present late in Nigeria. Orthodox and traditional means are usually first sought before hospital presentation, causing most patients to present late with advanced and incurable disease. Most times in this case, palliative care may be offered with chemotherapy. In operable cases, surgery may be offered.
In this group of patients features in keeping with advanced disease such as weight loss due to elaboration of cachexin (TNF alpha), malignant peritonitis, colo-vesical fistula, colo-vaginal fistula and a host of other features due to local invasion, tumor infiltration and distant metastasis are seen.
Histologic Subtype and Mode of Spread
The mucin-producing adenocarcinoma has a higher proportion among native Africans compared to Caucasuians (it occurs in native Africans in a percentage of thirteen to twenty; while it occurs among Caucasians in a percentage of four to six) . It is also known to carry a bad prognosis . It is defined as a tumor displaying extracellular mucin in more than 50% of the tumor volume . New evidence is showing that mucin-producing adenocarcinoma may have a distinct biological and genetic identity compared with non-mucinous adenocarcinoma [23,24]. Patients with mucin-producing adenocarcinoma are usually younger [25,26]; which most Nigerian cases fall into due to average life span demographics. In addition, these tumors may have distinct mutations and cytogenic abnormalities [23,27], and may be less likely to respond to chemotherapy[28-30]. These tumors are commonly right sided [31-33], and associated with advanced disease [24,25,31,32], which holds true for most cases in Nigeria
Spread may be by;
- Direct infiltration, usually by a transverse means to encircle the bowel wall. Microscopically it does not spread beyond 5cm of the macroscopic edge longitudinally . Thus the affected segment must be resected at least 5cm beyond the tumor edge .
- Lymphatic spread first to the paracolic lymph nodes and through the intermediate nodes to the inferior and superior mesenteric lymph nodes . The frequency of lymph node metastases is directly related to the degree of penetration of the intestinal wall and the histologic grade of the malignancy and not necessarily the size of the primary lesion .
- Spread through the blood stream is usually through the inferior or superior mesenteric veins, and the portal vein; to the liver (33%), less frequently to the lungs (22%), adrenals (11%), kidneys and bone (11%) and the brain.
- Transperitoneal spread which may result in malignant peritonitis with ascites.
The role of diet in the epidemiology of colon carcinoma is one that has been extensively studied . Most traditional Nigerian diets are said to be protective due to its high fibre, mineral and vitamin content from locally available fruits and vegetable, high spice and pepper content , which translates to higher antioxidant levels. Local Nigerian diets are majorly carbohydrate based which has been shown to have protective effects too . The high sunlight exposure Nigeria enjoys , appears to afford us more vitamin D, which is colon carcinoma protective.
The increasing incidence of colon carcinoma may be traced to adoption of westernized diets due to affluence. Most westernized diets have a low fibre and high fat content, which has been repeatedly shown to be a risk factor for colon carcinoma [37,38]. Intake of fruits and vegetables is reducing among Nigerians, with a concomitant reduced intake of minerals, vitamins, antioxidants and fibre contained in them, which are cancer protective .
The increasing adoption of tobacco smoking among Nigerians may also account for an increasing incidence of colon carcinoma .
Excessive alcohol intake has also been shown to be a risk factor for colon carcinoma and gastro-intestinal cancers in general, it is thought to be due to production of acetaldehyde which is a known carcinogen [35,36]. Due to increasing affluence among Nigerians, alcohol consumption is on increase.
Adoption of sedentary lifestyles with reduced physical activity is a risk factor for obesity. Obesity has been linked with colon carcinoma development [37,38]. Sedentary lifestyles are associated with less sunlight exposure, which amounts to less vitamin D in the body, with therefore an increased colon carcinoma risk, since vitamin D is known to be colon carcinoma protective .
The adoption of westernized lifestyle has been linked to increasing affluence among Nigerians and an ever increasing influx of foreign processed foods; most of which are associated with cancer risks, from developed countries into Nigeria.
Modality of treatment to be used is governed mainly by the stage of presentation and site affected.
Surgical treatment 
- Caecum, ascending colon and hepatic flexure; right hemi-colectomy, that is resection of the last 15cm of the terminal ileum, ascending colon and proximal two-thirds of the transverse colon with ileo—transverse anastomosis
- Transverse colon; resection of the transverse colon and both flexures
- Splenic flexure; left hemi-colectomy that is resection of the distal colon and distal two-thirds of the transverse colon.
- Descending colon; same as splenic flexure, but a more radical resection with removal of the pelvic colon is preferable.
- Pelvic colon; pelvic colectomy with or without left hemicolectomy
Treatment is most commonly by open abdominal surgery using diathermy, stiches and staples.
It is given preoperatively if the tumor is tethered or with evidence of extra-peritoneal spread and/or positive lymph nodes or post-operatively if a tumor turns out to be Dukes’ B2 or C . Radiotherapy may also be offered as a palliative measure in advanced disease.
5- fluoro uracil, an antimetabolite cancer chemotherapeutic agent is the major agent used. Leucovorin is usually added as an adjunct due to the associated risk of bone marrow suppression which may cause severe neutropenia. Other agents which may be used in combination with 5-flouro uracil, include the platinum based chemotherapeutic agent, oxaliplatin and irinotecan, a topoisomerase 1 inhibitor.
Bevacizumab is a humanized monoclonal IgG antibody which binds and neutralizes vascular endothelial growth factor (VEGF), which has shown so much promise with its use in the western societies, but with limited use in Nigeria due to cost implications.
Even though not yet realistic in this environment due to relatively low incidence rate, it is commonly practiced in high risk groups in the western societies, where it has become of public health concern. It includes;
- Fecal occult blood sampling
Colon carcinoma a major cause of morbidity in the developed climes and is gradually taking its root in Nigeria in particular, and Africa as a whole. This has been largely due to adoption of westernized lifestyle due to increasing affluence among Nigerians. Control and preventive measure must be put in place to stem this growing problem which has the potential to take its toll in Africa, being a resource poor environment.
I want to specially acknowledge Dr. D.O. Irabor; Consultant Gastro-Intestinal Surgeon, who has spurred my interest in the field of gastro-intestinal surgery due to his prowess as a teacher and great skill as a surgeon. I also appreciate him, for accepting to be the Supervising Consultant of this review article, and for being my mentor and role model.
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