Biology

Rectal cancer denotes the carcinoma that affects the rectum. Rectum is the lowest part of the colon. Rectum is the lowest part of the colon which connects the large intestine to anal canal. Rectum usually serves the purpose of storage of formed stool hence helping out in the preparation for final evacuation of the formed stool. In the literature, rectal carcinoma is usually regarded as a combined entity with cancer that affects the entire colon hence denoted sometimes as colorectal cancer. The disease state can be considered as an important public health problem worldwide.

Discussion
Epidemiology
Cancer is a leading cause of death in worldwide irrespective of the country or continent. About 40,000 new cases of colorectal cancer are usually diagnosed per year in the United States while the combined figure for colorectal cancer as a whole entity is about 150,000 new cases (emedicinehealth, 2010). Although there are various types of rectal cancer, the most implicated or most found to occur in America is the adenocarcinoma which is the type of rectal cancer that arise directly from the mucosa lining the rectum. It has also been found that this cancer has high rate of metastasis to other part of the body making it spread fast especially via lymphatics to other part of the body (emedicinehealth, 2010).

Anatomy of the rectum
Rectum has three main parts which are the mucosa, muscularis propria and mesorectum. The mucosa is the innermost part of the rectum, lines the lumen and its compose of glands that helps moisturize the mucosa by secreting mucus hence aid the easy passage of newly formed stool. The next layer which is outside the layer of the mucosa is the muscularis propria and its the middle part, made up of smooth muscles that help regulate the shape of the rectum and also control the movement of the stool within the rectum hence very important in the motility of the rectal content. Mesorectum is the outermost layer of the rectum and it consists mainly of fatty tissue. Apart from all the three part of the rectum, lymph nodes also surround the rectum and tend to help in the defence system of the body.

Fig 1. Shows the anatomy colon and rectum which is affected by cancer
Etiology and risk factors of rectal cancer
There is actually no main etiology of rectal cancer but there are several implicated risk factors that have been identified to play a major role in the initiation of the condition. Some researchers have shown a relationship between age, family history and the risk of developing rectal cancer. Individuals of 40 years of age or above have been found to be at an increased risk of developing rectal cancer while hereditary has been found to play an important role because of conditions such as familial adenomatous polyposis which increase the chances of having rectal cancer (cancercompass, 2010). A personal history of any of the following colorectal cancer, polyps in the colon or rectum or cancer of the ovary, endometrium or breast have all been attributed to increase the risk of developing rectal cancer(cancercompass, 2010).

Considering the rate of all these risk factors in our society and the influence of hereditary, chances of developing rectal cancer are bound to be on the increase. The unusual presentation of this type of cancer also makes it difficult to diagnose on time hence predisposing the affected individual to a fully established case of the carcinoma before such an individual will have the opportunity of being diagnosed and treated.

The clinical presentation of rectal cancer can simply be deduced from the affectation of its role in the digestive system. The common clinical features of this condition are diarrhoea, constipation, excessive stooling (all can simply be referred to as change in the bowel habit). Theres general abdominal discomfort, loss of appetite, weight loss, malaise and melena (blood in the stool).

Pathogenesis
Molecularly this condition usually starts with the mutation of signalling pathway known as the Wnt signalling pathway. This mutation can either be acquired or inherited. The gene that is usually mutated is the APC gene, it is this gene that is responsible for production of the APC protein which serve as a break on the Beta catenin protein and when this pathway is deficient, beta-catenin performs abnormally, moving into cells and causing several havocs. The disease then begins as a benign adenomatous polyp which will later transform into adenoma characterised with high grade dysplasia and subsequently progressing into an invasive cancer (Markowitz  Bertagnolli, 2009).

The influence of the damage caused by rectal cancer has a major impact on the metabolic and physiologic status of the individual. Several metabolic pathways will be affected while some of the current treatment modalities are targeted at the cellular. Rectal cancer which leads to diarrhoea and constipation usually lead to electrolyte imbalance because of loss of fluid and electrolyte and instant replacement by the individual is usually compromised by the associated abdominal discomfort characterised by frequent gas pains, fullness or cramps.

The electrolyte imbalance compromise several functions in the host if nothing is done on time to save the situation. For instance increase loss of potassium and sodium will ultimately affect the action potentials the neurons in the body of the patient needed for coordination hence it could lead to a state of coma and some other neurological deficit that may have a long or short term effect on the individual.

Treatment
There are different treatment modalities that have been formulated for the management of this type of cancer. The three main treatment modalities are the surgery, radiotherapy or chemotherapy. Several factors actually determine the choice of treatment modalities.  These factors include the extent of the lesion, the histological variants of the cancer cells and the absence or presence of metastasis to other region.

Out of all the available treatment modalities, its only the chemotherapy and the radiotherapy that actually target the cellular level of the lesion. Surgery is only instituted to respect the lesion and it is the most common form of treatment modality that is used to manage rectal cancer cases. In most cases, chemotherapy and radiotherapy are usually used as adjunct to surgery. Radiotherapy makes use of high energy x-rays to destroy the cancer cells and the major types that are used could either be the internal or external radiation forms. Chemotherapy targets the cells directly and either stop them from dividing or kill them straight hence tend to attack cancer cells with the body of the host.

In managing rectal cancer, palliative mode of treatment should be instituted in advance cases of the condition (Baigre  Berry, 2005), this is because of the effect of such treatment modality on associated local symptoms. The method has been found to provide quick and effective amelioration of the patient symptoms (Baigre  Berry, 2005). Treatment methods in managing rectal cancer have been considered to be slowly developing within the past 30 years (Lucas  Thorson, 2009). In contrast, the recent understanding and contemporary descriptions of advanced preoperative chemotherapy and radiation have contributed greatly to rapid revolution that is now being experience in the areas of managing the ailment.

Side effects of treatment
There are several side effects that are associated to the various treatment modalities for rectal cancer. For instance, the side effects of surgery are usually dependent on the extent of the surgery and the general status of the patient before the surgery. Complications that could result from the surgery include bleeding, damage to nearby organs during the operation, scar tissue formation and infection. The side effects of chemotherapy tend to be diverse because those drugs do affect the normal cells. Side effects of chemotherapy include diarrhea, nausea, vomiting, loss of hair, loss of appetite, fatigue and mouth sores. Radiotherapy has the following side effects such as problems controlling bowels, bladder irritation, tiredness or skin soreness.

Conclusion
Rectal cancer is one of the top leading causes of death in most western world. The burden associated with this condition can be attributed to its local and systemic symptoms and the ability of the cancer to metastasize to other part of the body. Considering nature of the condition, early diagnosis is essential for good prognosis. Preventive measures that focused on reduction of risk factors should also be encouraged so as to reduce the prevalence and incidence of rectal cancer in our society.