Experiments on the cause of the rabbit carcinomas derived from virus-induced papillomas. I. Propagation of several of the cancers in sucklings, with etiological tests.

Three out of four carcinomas arising from rims-induced, rabbit papillomas have grown well after transplantation to sucklings. Two were propagated serially, and it seems likely that all could have been maintained indefinitely had litters been available of newborn animals of the sort in which they arose. These successes are the more worthy of note because of the well-nigh uniform failure of similar growths on transfer to adults. The tumors enlarged with great rapidity in the sucklings, were extraordinarily destructive, and two of them metastaslzed within a few weeks. Many efforts were made to extract causative agents from the three carcinomas, on the assumption that these might be due to variants of the Shope virus. Highly favorable conditions for the demonstration of this latter were provided in the tests; yet their outcome was wholly negative although all of the cancers derived from papillomas caused by "recoverable" strains of virus, and although one of them appeared to be consequent upon only the slightest of alterations toward malignancy on the part of the papilloma from which it came. Extracts of another of the cancers, an anaplastic, squamous-cell carcinoma devoid of any morphological sign of the influence of the Shope virus, yielded typical virus papillomas on several occasions. The wholly negative results with the third cancer must be considered in the light of the fact that the "recoverable" strain of virus causing the papilloma from which it originated could no longer be recovered from such growths on collateral test.