In Tumor, a book by Anna Leahy, the author discusses the nouns "tumor" and "cancer":
The word tumor comes from the Latin for swelling. Indeed, a tumor is an overgrowth, a mass of tissue too large or unseemly for the body’s own good. Cells proliferate wildly and clump into something that doesn’t belong. The medical term for such a thing inside the body is neoplasm, which comes from words meaning new growth. A tumor is not necessarily cancer, and cancer is not necessarily a tumor. A tumor is new and different. Sometimes, it seems all the same, only more—much more—but the unfamiliar, the previously untraveled, makes all the difference.
To tell the truth, I can't get the whole meaning of this sentence, though I understand the meaning of each individual word!