Delay of tumor growth in hamsters treated with lynestrenol and effect of Staphylococcus aureus Cowan A

The action of lynestrenol, a synthetic progesterone-like substance, was studied in Syrian golden hamsters inoculated with cells transformed by herpes simplex virus type I. Daily ip injections of 1 mg lynesterol/kg delayed tumor growth. Lynestrenol alone only slightly increased the survival of the animals. This effect was more marked when the animals were also given injections of Staphylococcus aureus Cowan A. Survivors showed an increased resistance to challenge with infected cells. Hamsters previously given injections of killed transformed cells and then challenged with living cells showed a facilitation of tumor growth. This facilitation was inhibited by lynestrenol alone or combined with S. aureus Cowan A.