Although the origin of the term ?cancer? is not clear, cancer is responsible for nearly 13% of all natural deaths in the world. To better understand how cancer develops it is important to understand the concept of apoptosis (or programmed cell death). The human body produces millions of new cells each day, and each cell has an inbuilt mechanism that checks for any genetic defects and defective cells are destroyed by the body. Occasionally, cells with genetic defects survive and begin replicating. The defective cells are aggressive (grow and divide without respect to normal limits), invasive (invade and destroy adjacent tissues), and/or metastatic (spread to other locations in the body).
Cancer cells are resistant to apoptosis or in a nutshell do not know when to die. There has been considerable debate on what triggers the genetic mutation that protects cells from apoptosis. It is believed that genetic abnormalities are usually a result of carcinogens like tobacco smoke, radiation, chemicals and infectious agents (some studies have also linked certain viruses with cancer). Since there are numerous intricate and complex cellular interactions that lead to cancer, the exact mechanism of the development of a cancerous cell is unknown.
Genetic abnormalities usually affect apoptosis by triggering two classes of genes. Oncogenes give cells abnormal properties that impart cells resistance to apoptosis, such cells are hyperactive, and are very aggressive in nature. On the other hand, tumour suppressor genes are often deactivated in cancer cells, and such cells continue to produce defective copies of themselves, and their interaction with protective cells of the immune system is also erratic.
In essence, a cancerous cell is incapable of detecting inherited genetic defects, is resistant to apoptosis, is not destroyed by cells of the immune system and can create copies of itself at an accelerated rate.
Cancers are classified based on the type of tissue they originate from:
Carcinomas are malignant tumours derived from epithelial cells. Breast, prostate, lung and colon cancer are usually carcinomas.
Sarcomas are malignant tumours derived from connective tissue, or mesenchymal cells.
Lymphomas and leukaemia are cancers that are a result of uncontrolled growth of cells that form blood
Germ cell tumours are tumours derived from totipotent cells. Totipotent cells are usually found in the testicle and ovary in adults. In children and babies, such cells are found at the base of the spine and the body midline.
Blastic tumours are formed by cells that resemble embryonic tissue, and blastomas are mostly malignant in nature.
It is important to note that not all tumours are malignant in nature and benign tumours usually stop growing once they reach a certain size and are not always life threatening. Nearly 33% of all cancer cases in men are of prostate cancer, making prostate cancer the leading cancer among men. Breast cancer is the most common cancer in women and 32% of all female cancer patients suffer from breast cancer. Interestingly, lung cancer is the leading cause of cancer related deaths in the world.
Diagnosing cancer
Although initial diagnosis of cancer is carried out based on symptoms exhibited, the symptoms of cancer are so varied that diagnosing cancer based on the symptoms alone is next to impossible. Patients usually undergo blood tests, cancer marker tests, CT scans and X-rays before a biopsy. Endoscopy has also become an invaluable tool in cancer diagnosis.
However, the most effective means of diagnosing cancer is by carrying out a tissue biopsy. A tissue biopsy involves extraction of a small sample of the ?suspect? tissue. Once the biopsy is performed, the tissue is studied by a pathologist for cancer characteristics. Advances in surgery, like keyhole surgery have made tissues biopsies safer and patients do not have to endure long recuperation times after biopsies anymore. A biopsy is also necessary for positive classification of the type of cancer.
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