Apparently the word is of ancient origin, a latin translation from the greek word "carcinoma". Carcinoma originally meant any deep ulcer/sore that might’ve been malignant, as did it’s latin counterpart. The word also means "crayfish" or "crab", as some might have guessed. But anyway, the etymology of the word "cancer" is very old, and most likely originally included many other (macroscopically similar) conditions in addition to the actual carcinoma. Anyway, the "word" cancer is a latin derivation like you kind of suspect in your post. At least this is how I think it is 🙂