Biology of Disease

Prostate cancer cells have receptors for the active form of testosterone and their
growth requires a supply of testosterone from the testes. The aim of hormone
therapy is to lower testosterone levels. Some of the drugs used are analogs
of gonadotrophin releasing hormone (GnRH), examples being goserelin,
leuprorelin and triptorelin. Goserelin is administered as a subcutaneous pellet
while the others are injected subcutaneously or intramuscularly in liquid form.
Other drugs used are antiandrogens, which block the interactions of hormone
and receptor. The side effects of hormonal therapy include sexual impotence,
flushes and sweating which may be reduced by intermittently stopping and
starting the therapy.

The prognosis for men with prostate cancer is generally good, since this type
of cancer usually occurs in older men and grows slowly.

Colorectal Cancer

Colorectal cancer, otherwise known as bowel cancer, is one of the three most
common cancers in men and women, both in the UK and in the USA. In the
UK there are about 35 000 new cases each year, with a slight majority occurring
in men. Approximately 60% of new cases are cancers of the colon while the
remainder have cancers of the rectum. In the USA there are roughly 135 000
cases each year, about 70% being colon cancers. The five-year survival rate
for colorectal cancer is 50–60%. The vast majority of colorectal cancers are
adenocarcinomas and this section will concentrate on these. The remainder
fall into several groups as shown in Table 17.10.

Colorectal cancer Description

Adenocarcinoma 95% of colorectal tumors, they arise from mucus-secreting cells

in epithelium of GIT lining. Most produce mucin. Between 1 and

2% aresignet-ringtumors where the intracellular mucus pushing

nucleus to one side.

Squamous cell carcinoma arise from epithelial cells of GIT lining.

Carcinoid tumor rare, slow growing tumor of neuroendocrine origin.

Sarcoma majority are leiomyosarcomas arising from smooth muscle in GIT

wall.

Lymphomas 1% of colorectal cancers arising from lymphoid cells in GIT wall.

Table 17.10Types of colorectal cancer

The risk factors for colorectal cancer include increasing age, a diet rich in fat
and low in fiber, a history of inflammatory bowel disease and a hereditary
predisposition. More than 80% are diagnosed in those aged over 60 years. A
familial history of bowel cancer is also a strong risk factor as is the presence
ofpolyps. A polyp is a benign tumor that arises from the epithelium of the
GIT. Polyps range in size from a small bump to a lesion measuring 3 cm in
diameter; most are asymptomatic.

Adenocarcinomas are known to originate from pre-existing polyps and the
sequence of their development into a cancer is well documented. Individuals
with familial adenomatous polyposis (FAP), a rare condition responsible for
1% of colorectal cancers, have a mutated form of the adenomatous polyposis
coli (APC) gene. This gene encodes a protein that degrades B-catenin, which
activates growth-promoting oncogenes such as c-MYC. Mutations in APC lead
to the production of inactive B-catenin, hence oncogenes are continuously
activated. Patients with FAP are almost certain to develop colorectal cancer
in middle age and they are recommended to have their colon removed by

SPECIFIC TYPES OF CANCERS

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