I thought I remembered seeing the term used in one of the Socratic dialogs. A quick google turned up this, though not Socratic...

The doctors Hippocrates and Galen began to revolutionize medical thought by thinking about disease as a natural physical process, rather than one caused by magic and the supernatural. They had a profound influence on the treatment and understanding of disease for almost 1500 years. Hippocrates gave the name karkinos and karkinoma (the ancient Greek words for "crab") to a group of diseases that he studied, including cancers of the breast, uterus, stomach, and skin. The hard center and spiny projections of the tumors Hippocrates observed reminded him of the crustacean. "Cancer" means "crab" or “crayfish” in Latin. Indeed, cancer became a recognized diagnosis in this time period. Although Galen removed some tumors surgically, he generally believed that cancer was best left untreated.

http://www.chemheritage.org/EducationalServices/pharm/chemo/readings/timeline.htm