What’s the best definition of “cancer”?

We’ve talked before about the concept of neoplasia.

Just to refresh your memory: a neoplasm is a group of cells that started out from one single cell with a bunch of genetic mutations. These genetic mutations allowed that initial cell to multiply on its own – basically ignoring any of the normal cell signals that tell a cell to start or stop dividing. This means that one initial cell was able to divide into two identical cells, and then into 4, and then into 8…well, you get the idea.

Benign vs. malignant

Neoplasms can be benign (meaning, basically, that they stay in one place and can be relatively easy to treat) or malignant (meaning that the neoplasm is able to metastasize to far away places and is therefore usually much harder to treat). Those are simplistic definitions of benign vs. malignant – but that’s enough for right now.

Cancer

In this post, I want to define a word you’ve no doubt already heard many times: cancer.

The first thing I want to be sure you know is that “cancer” is not the same as “neoplasia.” As we just said, there are two big categories of neoplasia: benign and malignant. Cancer is a word that’s sometimes used to describe malignant neoplasms (but never benign ones). So far so good.

Wait, why do we use “cancer” like this?

The word cancer comes from the Latin word for crab (like the zodiac sign). Malignant tumors are called cancers because they adhere to anything they seize in an obstinate, crab-like manner.

Here is a gross image of a piece of breast tissue with breast cancer:

And just so you can more easily see what’s going on, here is the same image, with annotations:

You can actually see the breast cancer reaching out with crab-like tenacity into the surrounding fatty tissue.

Benign tumors don’t grow like this. They’re much more polite, and they grow in a way that pushes the surrounding tissue out of the way, rather than reaching out and infiltrating the surrounding tissue.

Bottom line

Malignant tumors are sometimes called “cancers” because they usually grow in an infiltrating way, reaching out into the surrounding tissue like a crab.