Squamous Differentiation in Mouse Mammae: Spontaneous and Induced

Abstract

DURING the course of a scrutiny of mammae of old breeding females of several inbred strains of mice in which either very few or no spontaneous mammary tumours had arisen, foci were found in one of the strains of apparently spontaneous squamous differentiation. This differentiation took the form of squamous epitheliosis in ducts and in acini. It was frequently, but not invariably, accompanied by scattered or massed secretory acini in mammary glands that elsewhere were completely involuted. The strain affected was the R III X, a subline of the Paris R III strain, which had previously been freed from the Bittner agent of heritable mammary tumours. A close scrutiny was being made to determine whether mammae of mice free of the agent and of heritable mammary carcinomas were devoid also of adenomas. The result of this first objective is incomplete since it entails survival of a sufficient number of spayed mice to determine the part played by ovarian hormones, but will later be reported. Another experiment in progress during the period of observation included an examination of mammae of young breeding females of the same R III X agent-free subline which had been treated by skin painting with methylcholanthrene with the object of inducing mammary tumours. The experience of many authors indicated that mammary tumours of various sorts would arise (Dobrovolskaia

Spontaneous Mammary Adenoma and Carcinoma in RIIIb Mice Deprived of Milk Agent

“…Cornification tests to exclude the possibility that oestrogen was being produced in suprarenals subsequent to ovariectomy were not done because they had been found to be unnecessary in adult mice in this strain on previous occasions. All 10 nipple areas were examined as previously described (Pullinger, 1947). Those containing hyperplastic nodules of any kind were mounted and kept.…”

“…It was not possible to subject all predominantly acinar new formations to serial section. Therefore they were judged to be purely or mainly acinar on the basis of the polarising test used before (Pullinger, 1949), and from experience of a total of 60 nodules derived from various surveys in hand and cut in serial section by the author.…”

“…Focal acinar proliferations were often but not invariably discretely lobular. The squamous-celled nodules found in old RIIIb females have been described and their origins discussed (Pullinger, 1949).In relation to the problem of the presence and action of the milk agent these squamous-celled proliferations are not relevant, for it is generally agreed that tumours due to Bittner's agent are characteristically acinar formations and that …”

“…The validity of such evidence would depend upon complete absence of spontaneous adenomatous nodules in the same strain deprived of agent. In sublines of the RIIIX strain (renamed RIIb in accordance with international usage), which had been freed from agent by cross-suckling, no nodules had been found in the mammae of young unmated females forcibly stimulated, but two hyperplastic nodules were seen in 2 out of 44 females of the old breeding stock (Pullinger, 1947). Doubt thus arose whether the cross-suckled sublines were in fact entirely agent-free or whether, in old females, these nodules had some other cause.…”

“…Focal acinar proliferations were often but not invariably discretely lobular. The squamous-celled nodules found in old RIIIb females have been described and their origins discussed (Pullinger, 1949).…”