Response of Hyperplastic Alveolar Nodule Outgrowth-Line D1 to Mammary Tumor Virus, Nodule-Inducing Virus, and Prolonged Hormonal Stimulation Acting Singly and in Combination

This paper presents evidence that the nodule-inducing virus (NIV) can participate in the production of neoplastic cell variants within the hyperplastic alveolar nodules in the mammary glands of BALB/c mice. The transplanted D1 nodule outgrowth had an increased tumor incidence and a decreased mean age of onset after infection with NIV. An additional increase in tumor incidence was achieved when D1 nodule outgrowths were infected with both NIV and the mammary tumor virus (MTV). Although prolonged hormonal stimulation produced by pituitary isografts, in the absence of MTV and NIV infection, failed to increase the tumor incidence in D1 nodule outgrowth, it exerted a synergistic effect when acting in conjunction with either MTV or NIV.