Above: Uncontrolled division of cancer cells. Image © istockphoto.com/selvanegra
Almost half of all Canadians will develop cancer in their lifetimes and one quarter of all Canadians are expected to die of the disease. But could you explain what cancer actually is? This article will help you understand the biological mechanisms behind how a normal cell transforms into a cancerous cell.
Did You know? Kidney cancer has been on the rise in Canada since the 1980s. This can be explained in part by increased rates of obesity.The cell cycle and proteins
Cancer can originate in any one of the millions of cells that make up your body. It begins with a disruption in the cell cycle, which refers to the different steps required for a cell to divide and replicate itself. Most types of cells have the the ability to stop dividing, either when they come in contact with other cells or when they run out of room because there are too many cells present. However, when a cell’s ability to stop dividing is disrupted, and it can no longer control how often and how many times it divides, the result can be lumps called tumours.
Many functions in your body, including the cell cycle, are regulated by proteins. At each step in the cell cycle, these large molecules ensure the cell remains healthy and keeps functioning properly. And when these proteins can no longer do their job properly, the replication of cells can get out of control.
Oncogenes and tumour suppressor genes
A protein’s function is determined by its genetic makeup. When this genetic information is disrupted, the job the protein is responsible for can also be disrupted. In particular, there are two types of genes that can affect the cell cycle and the development of tumours: oncogenes and tumor suppressor genes.
Proto-oncogenes, which are oncogenes in their normal, non-disrupted form, allow cells to proceed from one cycle to the next. This is is necessary for normal biological processes like growth and regeneration after injury. But when a proto-oncogene is altered and becomes an oncogene, it can produce a protein that does not function properly, causing cells to divide uncontrollably.
However, the production of oncogenes alone cannot cause a tumour. Tumour suppressor genes, which restrict the progress of the cell cycle, also need to be deactivated. In other words, it is not enough for a cell to begin dividing uncontrollably. The built-in mechanism that would normally put the brakes on that process also needs to be disabled.
Did You know? Over 30% of cancer could be prevented if more people adopted a healthier lifestyle and were immunized against cancer-causing infections like HBV (hepatitis B virus) and HPV (human papillomavirus).Benign and malignant tumours
Disrupted cells can actually lead to two different types of tumours: benign and malignant. Benign tumours are considered non-cancerous since they rarely cause serious health problems or threaten a person’s life. That is, unless they grow very large and interfere with a vital organ or tissue. However, benign tumours generally grow slowly, do not spread to other parts of the body, and do not come back after they have been surgically removed.
Malignant tumours are cancerous. They can vary in size and shape and grow uncontrollably, invading nearby tissues and blood or lymphatic vessels. As a result, they can interfere with bodily functions and becoming life-threatening. Cells from malignant tumours can also break off the original cell mass and spread to other parts of the body. Finally, malignant tumours can come back after they have been surgically removed.
There is no one single cause behind the cancer-causing damage affecting genes, proteins, and cells. In fact, a number of different factors are usually at play. These factors may be related to lifestyle (smoking, a high-fat diet, working with toxic chemicals, etc.), genetics (your genetic makeup, as well as some specific genetic conditions, can make you more susceptible to cancer), viruses (their genetic material can sometime affect the cells of infected people), environmental exposures (pesticides, fertilizers, etc.), and some forms of radiation (including UV radiation).
There are a number of changes that must occur in a cell to produce one that is cancerous, and there is a multitude of factors that can create those changes. Some of the factors, such as genetics, are out of your control. However, lifestyle changes like quitting smoking, using sunscreen, and using proper protection when working around chemicals can help you minimize the risk of cancer.
What is Cancer? (2015)
Stanford Health Care
General introduction to cancer, including symptoms, causes, types, diagnosis and treatments.
What Causes Cancer? (2015)
American Cancer Society
Links to information on the role played by genetics, tobacco, diet, physical activity, UV exposure, radiation and other carcinogens.
Types of tumours (2015)
Canadian Cancer Society
Brief overview of benign tumours, precancerous conditions, and malignant tumours.
Canadian Cancer Statistics (2013)
Canadian Cancer Society
Detailed of cancer rates, mortality and diagnosis, with a special focus on liver cancer.
10 facts about cancer (2013)
World Health Organization
Facts about cancer from an international perspective.
Trends in Incidence, Mortality, and Survival for Kidney Cancer in Canada, 1986-2007 (2014)
Prithwish De, Michael C. Otterstatter, Robert Semenciw, Larry F. Ellison, Loraine D. Marrett & Dagny Dryer, Cancer Causes & Control 10, 1271–81.
Article based on data from the Canadian Cancer Registry and the Cancer Incidence Reporting System, showing a significant rise in kidney cancer rates.