There are times as a scientist where you find yourself saying things like “Holy Cow! Really?! No way!” You hope that these sorts of exclamations come during your own investigations in the lab but, really, it’s most often the discovery of another daring scientist that totally blows your mind.
Take, for example, recent discoveries about cancer and how it starts.
As a grad student, I was taught that tumors form when a single mutated cell begins to proliferate…a lot. To better understand this, a healthy cell reproduces by splitting in half and creating two copies of itself. These cell copies go on to create two copies of themselves and so on. This process is called cell division. Normal cells divide in a very controlled way and they know when to stop.
Cancer cells, in contrast, incessantly and persistently reproduce. They keep undergoing cell division and ignore signals telling them to stop, that the food and nutrients have started to run out, that they are crowding the space, and bothering the neighbors. A tumor then forms at the site where a cancer cell and all of its cancerous progeny have taken up residence. In this way, tumors are not dissimilar from a big, dysfunctional family. All the cells are related and each is wreaking havoc.
A recent paper in the journal Cancer Cell from Melo et al. (2014) describes a totally different model for cancer progression. And, for the sake of this post, I’m going to call it the “zombie” model. They argue that cancer cells have a way to “infect” neighboring cells, turning otherwise healthy cells into cancer cells.
In this study, they found that breast cancer cells secrete (for lack of a better word) little blobs, called exosomes or extracellular vesicles. Many cell types secrete exosomes, which are actually small spheres of plasma membrane wrapped around proteins and genetic material. Melo et al. found that exosomes derived from breast cancer cells have all the machinery and material necessary to “turn off” tumor suppressor proteins in healthy cells and were sufficient to start tumor formation. Not only that, they found that breast cancer cells secrete way more exosomes than healthy cells.
So, in the zombie model, exosomes might be a mechanism that cancer cells use to create a zombie-like hoard of other cancer cells. Imagine “28 Days Later,” only this time, the zombies don’t need to bite the victims. Just by being in the vicinity of the zombie, people would be at risk for turning into one of them. That’s a terrifying thought.
This finding has implications for how cancer progresses and spreads in the body since exosomes can be isolated from blood (think a new model for metastatic or persistent cancers). Plus, it could radically change how cancer is treated, by targeting exosomes in addition to the cancer cells themselves.
What all of this really goes to show you is that even in a very well-studied, fairly well-understood field like cancer biology, scientists still have a lot of work to do. There are lots of surprises lurking in the human body.