Cancer

This post is mainly going to be a quick overview of what cancer is and what the different types of cancer are, plus an outline of some of the treatments used. Obligatory disclaimer: I'm not a doctor, so don't take any of this as medical advice. If you have any concerns about anything medical... SEE. YOUR. DOCTOR.

Another quick note: there's a high likelihood that a lot of new scientific discoveries regarding cancer have been made since my sister's old human bio book was published 11 years ago. If there's any outdated information in here, please let me know, and I'll fix it.

Let's begin!

What is Cancer?

Cancer consists of many diseases with several characteristics in common, perhaps the most prominent being the uncontrolled division of cells, which results in an abnormal mass of tissue known as a malignant tumour or a malignant neoplasm. Furthermore, these cells do not differentiate as much as the normal tissue cells around the tumour, allowing the cancerous cells to be identified under the microscope. Malignant cells are able to spread to other parts of the body and cause secondary tumours in a process known as metastasis.

It is important to note, however, that not all tumours are cancerous. Benign tumours do not spread to other parts of the body, as their cells cannot invade normal tissues or blood or lymph vessels. They are usually easily removed; however, they can still be quite dangerous if they exert pressure on vital organs.

Types of Cancer

There are four main types of cancer:

1. Carcinomas- form from epithelial cells on the inner and outer surfaces of the body (see my post about tissues for more info on epithelial tissue). Around 90% of cancers are carcinomas.
2. Sarcomas- form from supporting tissues such as cartilage, fatty tissues, bones and muscles. Around 5% of cancers are sarcomas.
3. Lymphomas- solid tumor masses formed from cells of blood and lymphatic origin.
4. Leukaemias- cancer cells circulate in the bloodstream. Like lymphomas, they arise from cells of blood and lymphatic origin.

Causes of Cancer

Not all cancers have known causes, but we do know that there are some factors, known as carcinogens, that can trigger the growth of tumours. Normally cancer only occurs after long-term exposure to a carcinogen. Cancer can, however, develop many years after exposure has ended.

There are two stages of the development of a tumour: the initiation stage, in which some cells are changed irreversibly from exposure to the carcinogen; and the promotion stage, which is where the initiated cells start dividing and become a malignant tumour.

It is not so clear why cancerous cells divide in an uncontrolled manner after exposure to a carcinogen. (Well, at least it wasn't clear 11 years ago. It might be clear now.) However, research has shown that one cause of cancer is damage to a set of genes called proto-oncogenes, which then mutate to become oncogenes which promote the uncontrolled division of cells. This could be from random mutation, inherited genes or from the effects of carcinogens.

Without further ado, let's look at some known carcinogenic agents:

• Ultraviolet radiation can cause skin cancer, which is why health authorities and stuff tell us to "slip slop slap" in summer (except now it's like "slip slap slop slide shade"- slip on a T-shirt, slap on a hat, slop on sunscreen, slide on some sunnies and stay in the shade). Most skin cancers are slow-growing and don't spread. However, cancers that develop from the melanocytes (pigment cells) in the skin can form melanomas,which grow and spread very quickly.
• X-rays can cause cancer, but don't worry too much if you require one- modern machines don't produce too much radiation so there is very little risk from routine clinical use.
• Ionising radiation from exposure to radioactive substances, such as radium and uranium, can cause cancer.
• Some viruses are linked with some cancers. For example, human papilloma virus (HPV) is linked to cervical cancer and anal cancer as well as some other types of cancer. (Fortunately, there's two vaccines against some strains of HPV. They only protect against a limited number of strains, but these strains include the strains most likely to cause cancer, so if you want to avoid these cancers as much as you can, this might be worth a... shot.)
• Some chemicals, such as arsenic, asbestos and tobacco, can lead to cancer. Simple precautions (e.g. using safety equipment, limiting consumption etc.) can be taken to reduce the risk.

Symptoms of Cancer

Since cancer comes in so many different varieties, the symptoms of cancer vary considerably. There are, however, some warning signs that you can look out for:

• Lumps anywhere in the body (particularly in the breast, neck, testicle or armpit)
• Chest pain, chronic cough, blood in phlegm, hoarseness
• Changes in bowel or bladder habits
• Blood in faeces or urine
• Unusual bleeding or discharge (includes irregular or heavy periods)
• Chronic indigestion or difficulty in swallowing
• Sores that don't heal (e.g. a chronic ulcer)
• Changes in warts or moles
• Unexplained weight loss

Diagnosing Cancer

There are several different techniques used to identify tumours. Here's a quick overview:

• X-rays- yes, I know that I said that they can cause cancer if used a lot (much much more than in routine clinical use), but they're also useful for detecting tumours.
• CT (computerised tomography) scans
• Ultrasound- detects cancers in the abdomen. Cells in the tumour reflect ultrasonic waves differently.
• Endoscopy- inserting a camera-like instrument into the body to look for unusual growths. During this process, smaller growths can be removed.
• Biopsy- a sample of cells from a suspected tumour are removed and examined under a microscope. Surgery can be used to remove the tissue sample, or another technique, called fine-needle biopsy, uses a fine hollow needle to withdraw the sample.
• Smear tests- check for cells in body fluids such as urine and mucus.

Cancer Treatments

Several treatments are used in order to get rid of the tumour and stop the cancer from spreading. If this isn't possible, treatment is mainly aimed at reducing the symptoms of cancer- this is known as palliation.

The three main treatments are surgery, radiation and chemotherapy. Surgery is useful for removing small, localised tumours. Radiation (via X-rays or gamma rays) can kill or inactivate some cancer cells. (Yep, by the looks of things certain carcinogenic agents can actually treat cancer if used in the right hands...) Chemotherapy uses certain chemical substances to kill off the cancer cells.

Preventing Cancer

Although there's no 100% surefire way to prevent cancer, there are things that you can do to reduce your risk:

• Avoid smoking
• Slip, slop, slap, slide, shade (i.e. keep your body covered with clothing, use sunscreen, wear a hat and sunglasses, stay in the shade)
• Be especially careful to stay in the shade during the hottest parts of the day (if possible)
• Eat adequate amounts of fibre and not too much fat
• Make sure to get the appropriate checks for your gender and age (mammograms and Pap smears for women, prostate cancers for older men)
• Use protective clothing when handling dangerous chemicals
• Get vaccinated against HPV (okay, maybe I shouldn't be preaching this one because I haven't actually been vaccinated *shifty eyes*)