Observations on the Mode of Origin of the Fibroadenoma of the Mammary Gland in the Rat and on the Delayed Retrogression of the Mammary Gland after the Period of Lactation

Abstract

Our previous observations (1) prove that the fibroadenoma of the mammary glands is a typical new formation in rats, which is of considerable interest in the analysis of tissue and tumor growth. It is, therefore, of importance to record data which tend to throw some light on its mode of origin. The following observations represent a first attempt in this direction. At the same time they give some information about the processes which lead to the retrogression of tissues that have proliferated; they show in particular how a delayed retrogression of the mammary gland may be compensated for, and present, furthermore, an interesting analogy with certain cirrhotic conditions found especially in the liver. A female rat from a stock inbred for eleven generations was received from Granby, Massachusetts, having been sent there from the Wistar Institute in Philadelphia. She was about twenty to twenty-one months old and had given birth to three young ones about three to three and one-half months previously. She had suckled the young, which had developed in a normal manner. On examination, it was found that the mother had four tumorlike masses at the site of the mammary glands. One was situated posterior to the right front leg; on cutting this was found to be a cyst filled with rather thick yellow fluid, which represented apparently autolysed material. No putrefaction had taken place. The cyst measured approximately 8 by 10 mm. in two diameters. In the region toward the right hind leg was found a larger cyst, measuring approximately 10 by 20 mm., which contained clear fluid. On the same level with the latter, on the left side of the animal, was a similar cyst, and still further caudad, in the region of the most posterior left mammary gland, there was a solid mass instead of a cyst. The diameters of the cyst and of the solid mass on the left side were intermediate between those of the two cysts on the right side. Otherwise the animal appeared normal. The ovaries were of the average size, the uterus fairly large but within the limits of normal variations.