The Walker carcinosarcoma was inoculated into the uterine lumen of the following six groups of rats : (1) Normal oestrous cycles, (2) ovariectomized, (3) ovariectomized + 2 mg progesterone daily, (4) ovariectomized + 2 mg progesterone + 2 μg oestradiol-17β daily, (5) ovariectomized + 2 mg progesterone daily + a single injection of 0·2 μg oestradiol-17β on the day of tumour transplantation, and (6) pseudopregnant, Day 5.
Whilst the tumour grew well outside the uterus in all groups, tumour tissue only invaded the uterine wall in Groups 5 and 6. Growth was most marked in the pseudopregnant animals, where the tumour was actively invading the anti-mesometrial decidua. In Groups 3 and 5, the uterine lumen was full of extravasated blood and polymorphonuclear leucocytes, whereas in Groups 1, 2 and 4 the uterus appeared normal, with no signs of any tissue reaction.
It is concluded that the tumour behaves very like the blastocyst; its ability to survive within the uterus is hormone dependent, whereas it can develop outside the uterus irrespective of the hormonal environment. The mechanisms by which a hostile endometrium can destroy the tumour are not known.
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