A contagious disease (also known as a communicable disease) is one that spreads from person to person, either through physical contact or through particles that travel through the air and are inhaled. Flu, chickenpox, measles, and hepatitis A are examples from a very long list of contagious diseases that cancer is not on!
How Cancer Can Be Transmitted Between People
Although it is found in abundance across the world (globally, Australia has the highest age-standardized cancer rate* and Niger has the lowest), cancer is not contagious in the human population.
The only way it can be transferred from person to person is through an organ transplant (if the donated organ contains malignant cells), from a mother to her foetus during pregnancy, or from twin to twin in the womb, but these cases are extremely rare. Only a few dozen cases of mother-foetus cancer transmission have ever been recorded and the risk of cancer being transmitted to an organ recipient is less than 0.1%.
Contagious vs Non-Contagious Cancer
The reason that cancer is not transmissible between people is that our immune systems are very skilled at recognizing foreign cells and destroying them before they have a chance to spread. However, other species don’t have as much luck; some cancers are contagious in non-human animals. There have been cases of cancer transmission in dog and bivalve populations, and the devil facial tumour disease, a type of contagious cancer, is threatening Tasmanian devils with extinction.
How Cancer Works
So, how does this dreaded disease take hold of its host? Unfortunately, it’s our own bodies that do the work. In The Body, Bill Bryson quotes Dr. Josef Vormoor as saying, “Cancers aren’t contagious. They are you attacking you.”
Cancer develops through errors that occur in the DNA of our cells as they grow and divide, or through damage to our DNA as a result exposure to carcinogenic substances. In 15 to 20% of cases, cancer is caused by a viral or bacterial infection. However, although viruses like Hepatitis B and Humanpapillomavirus can be transferred between people, the cancer that they (sometimes) make people more susceptible to cannot.
Keep Cancer Patients Close
So, if a fear of catching cancer has led you to distance yourself from people with the disease, rest assured, you can stop worrying. In fact, we recommend spending as much time as possible with people you know who have cancer because community is one of the keys to decreasing depression (something that cancer patients commonly struggle with, which you can read more about in our Impacts of Cancer on Mental Health blog post).
*The reasons that the ten countries with the highest cancer rates are all high-income countries can be attributed to lifestyle factors such as obesity, smoking, and alcohol consumption.