Cancer is not contagious — or is it? Although each person has some risk of developing cancer over their lifetime, we do not typically consider cancer to be an infectious disease that someone can “catch,” like the flu or a cold. There are some infectious diseases that can cause cancer, like HPV, which can cause cervical and other cancers. However, in those cancers, the virus moves from person to person — the cancer itself does not.
But new research suggests there is more to the story.
An Unexpected Discovery
When PNRI’s Michael Metzger, PhD started looking for the cause of an unusual outbreak of disease in clams, he assumed it was a virus transmitted from one clam to another. What he found, however, was shocking: disease transmission was traced back to cancer cells moving from one clam to another.
Cancer spreading as a cell from animal to animal is not completely unheard of — but it is exceedingly rare. “Animals have immune systems that we think should reject tissue from other organisms,” says Michael. “This cancer may have evolved to bypass the clam’s immune system.”
While scientists know of cases of communicable cancer in dogs and Tasmanian devils, those infections are always spread through direct contact (such as through bites). “In this case,” says Michael, “the cancer cell travels from clam to clam through the seawater that contains them both. It is a unique phenomenon.”
Why Do Some Clams Resist Cancer?
Though interesting in itself, what intrigues Michael most about the clam cancer is understanding the genetics that make some clams susceptible and others cancer-free. Though the sick clams catch the disease by exposure to the cancer cells in seawater, many of the clams remain perfectly healthy, even though they are exposed to the same seawater with the same cancer cells.
He believes this discovery could teach us about cancers in general. “By studying the genetics of these cancer cells, we can gain insight into how cancer evolves over time and how it interacts with our bodies’ own natural defenses,” Michael says. “Studying why some clams are resistant to this cancer may help us develop ways to treat cancer in humans.”