PRL and neoplasm: Figure 7C shows that addition of Doxy to the drinking water caused a strong acceleration of tumor growth of clone 2 relative to the controls, presumably because of the actions of locally produced hPRL. Whereas control tumors reached a plateau after 4–5 weeks, those driven by autocrine hPRL continued to grow, in agreement with our previous report on the tumor-promoting activity of autocrine PRL [17].