Enhancing effect of excess topical vitamin a on rous sarcomas in chickens

The right and left wing webs of 36 White Leghorn chickens were inoculated with varying amounts of Rous sarcoma virus (RSV), ranging from 5000-100,000 focus-forming units (FFU) per injection. Thereafter, the right wing webs were painted doily with topical 20% vitamin A pal- mitate in paraffin oil for 3 weeks. The contralateral wing web was left un­treated for a similar period, and 22.2% of the birds developed fibrosarcomas measuring 1-2 cm in diameter and weighing from 6-30 g. On the side treated with vitamin A, 52.8% of the webs had large tumors weighing up to 240 g and measuring from 6-13 cm in diameter. Tumors developed in 50% of the webs given smaller doses of RSV (5000-20,000 FFU) followed by topical vitamin A, as opposed to 15% in webs given similar small doses of RSV alone. The tumors developing after topical vitamin A were more aggressive both macroscopically and histologicolly. They infiltrated muscle and bone and even metastasized. They also had large amounts of muco­polysaccharides in the stroma. When the wings of 10 chickens were treated with topical vitamin A palmitate before injection of RSV, tumors weighing from 6-20 g developed in all treated webs, whereas tumors weighing from 1 -5 g developed in 6 of the 10 wing webs not treated with vitamin A. The results are attributed to the established membrane-labilizing qualities of the vitamin which probably enhance tumorigenesis, either by facilitating more effective entry of the virus into the tissues or by altering the structure and function of the virus and target cell in a manner more amenable to malignant trans­formation. —J Nat Cancer Inst 48: 407-416, 1972.