Adenovirus type 9-induced tumorigenesis in the rat mammary gland related to sex hormonal state.

Adenovirus type 9 was inoculated sc into newborn Wistar/Furth rats, divided into four groups: (1) six male rats, not treated further; (2) 11 male rats, castrated at 4 weeks of age; (3) 12 male rats, castrated at 4 weeks of age and subsequently treated repeatedly with estrogen; and (4) 12 female rats, not treated further. All of the rats in group 3 developed mammary hyperplasia and tumors (fibroadenomas and lipomas), in some cases with malignant histologic structure. Rats in group 4 developed similar mammary tumors, but with later appearance and significantly slower growth. A fifth group of rats, not virus inoculated but castrated and estrogen treated as in group 3, did not develop any demonstrable mammary lesions. The results show that the effects of the virus on the mammary gland are dependent upon an estrogenic background, which by itself cannot cause tumor development in males. It is suggested that viral DNA is incorporated into the cellular DNA in such a way that it influences the synthesis and/or activity of steroid receptors, triggering tumor development.