Effect of human placental lactogen on growth of carcinogen‐induced mammary tumors in rats

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Abstract
The effect of exogenous administration of human placental lactogen (HPL) on 7,12‐dimethylbenz(a)anthracene (DMBA)‐induced mammary tumors was studied in female Sprague‐Dawley rats. Twice daily injections of 1 or 2 mg HPL for 20 days showed marked stimulation of appearance and growth of mammary tumors and of normal mammary gland growth not only in intact but also in adreno‐ovariectomized rats. These results suggest that placental lactogen plays an important role in the growth of DMBA‐induced mammary tumor of rat and that it acts on mammary tumorigenesis during pregnancy both directly and indirectly through its promotion of progesterone secretion by the ovary.