why is cancer called cancer

[drhess]

What do cancer cells have to do with Cancer the symbol or astrological sign?

[King_Friday]

Why is it called a building when it’s already built?

[Scruloose]

One of the definitions at www.dictionary.com offers this:

3. (Med.) Formerly, any malignant growth, esp. one attended with great pain and ulceration, with cachexia and progressive emaciation. It was so called, perhaps, from the great veins which surround it, compared by the ancients to the claws of a crab. The term is now restricted to such a growth made up of aggregations of epithelial cells, either without support or embedded in the meshes of a trabecular framework.

Source: Webster’s Revised Unabridged Dictionary, © 1996, 1998 MICRA, Inc.

[Walloon]

A slightly different explanation is that the ancients compared the hardness of a cancerous tumor in the body with the shell of a crab.