Synergistic tumor promoter effects of estrone and progesterone in methylnitrosourea-induced rat mammary cancer

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Tumor promoter effects of steroid hormones were tested in ovariectomized rats treated with the tumor initiator, methylnitrosourea. Continuous treatment with low doses of estrone induced tumor in 55% of experimental animals while intact control animals had a 96-100% incidence. Although progesterone alone produced no tumors in ovariectomized, methylnitrosourea-treated animals, estrone and progesterone acted synergistically, inducing tumorigenesis in 88% of treated rats. These results point to an important interaction between estrogens and progestins in promoting mammary tumorigenesis.

Original languageEnglish (US)
Pages (from-to)113-119
Number of pages7
JournalCancer Letters
Issue number2
StatePublished - May 28 2002



  • Estrogen
  • Mammary tumorigenesis
  • Methylnitrosourea
  • Progesterone
  • Rat

ASJC Scopus subject areas

  • Cancer Research
  • Molecular Biology
  • Oncology

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