In 1863 Virchow* stated that it was practically impossible to give a satisfactory definition of a tumor, and many writers since that time have unwittingly proven the truth of that statement. In dealing with epithelial neoplasms we may, however, say that any autonomous growth of epithelial cells, or of cells derived from the epithelium, constitute a neoplasm. We are not dealing with inflammatory masses or with cysts, although either of these conditions can, and do, give rise to tumors, sometimes clinically indistinguishable from true neoplasms.
Prickle-celled cancer originating In an old lupus vulgaris lesion. (Collection of Dr. M. Heldingsfelrf).