Modern cancerology is based on the oncogene concept. This is rather new. The idea of the oncogene, however, is old, and can be traced back to two sources, namely to “cancer families,” reported in 1866 by P. Broka, and to “virus induced” neoplasia, detected by P. Rous in 1911. A gene which is—to my knowledge—the first reported oncogene by definition was detected in the little ornamental Mexican fish Xiphophorus by Myron Gordon, Curt Kosswig, and Georg Häussler in 1928 when they observed the terrible hereditary melanomas that we are now coming to understand and to compare with other kinds of neoplasms in Xiphophorus and in mammals, including humans. Although the Xiphophorus model was always modest in its claims, it has—sometimes too early in its history—contributed many facts to the present concept of neoplasia.