The Unusual Occurrence of a High Incidence of Spontaneous Mammary Tumors in the Albany Strain of Rats

Abstract

Although the spontaneous occurrence of mammary tumors in rats is by no means uncommon, the incidence of 50.9 per cent which we have observed among the females of a small breeding colony during a period of eighteen months is much higher than any we have found reported in the literature. This “endemic” development of tumors in a strain of rats which previously had not shown them, with a coincident progressive decline in fertility, indicates that fundamental changes have taken place in this strain which may be of significance in the study of mammary gland neoplasia. Furthermore, studies now in progress disclose certain abnormalities in the sexual cycles of the female rats of this strain, and in the cytology of the pituitary gland. Some results of the latter studies are given in preliminary form in a later section (page 382) of this report. The present communication is for the purpose of recording, as a basis for subsequent reports, certain general information relating to this strain of rats—to be referred to hereafter as the Albany strain—and to describe the different types of tumors which have appeared spontaneously in animals belonging to it.