Induction of Cancer in Suckled and Unsuckled Female Rats

Abstract

SPONTANEOUS mammary carcinomas are a very rare event in female Sprague–Dawley rats¹, but this type of tumour can be produced easily and rapidly by repeated administration of 3-methylcholanthrene (3-MC) given by stomach tube². The neoplasias are more easily produced in young than in old rats and regress under appropriate hormonal modifications. Ovariectomy, hypophysectomy and critical amounts of œstrogens and gonadotropins are effective means of inhibiting neoplastic proliferations^2,3. Tumours of this kind are known as hormone-dependent. The hormonal conditions during pregnancy are of great significance in growth of tumour. It has been shown that rat mammary tumours appear more rapidly when 3-MC feeding is followed by pregnancy and the incidence of mammary cancers is reduced if the carcinogen is given during pregnancy. No induction of tumours is observed by giving 3-MC during lactation^4,5. Also, in mice the influence of pregnancy and lactation on 3-MC induction of mammary tumour has been stressed⁶.