CYTOPLASMIC INCLUSION BODIES IN CORTISOL-TREATED MAMMARY TUMORS OF C3H/Crgl MICE

The purpose of this note is to emphasize and augment published descriptions of cytoplasmic inclusion bodies in mouse mammary tumors. First noted by Borrel in 1903, eosinophilic bodies were studied in some detail by Gu~rin (1955). Gu&in found inclusions most often in mammary tumors developing after whole-body irradiation of 3to 6-month-old female mice of low-tumor strain IC, and in some cases in spontaneous tumors. The present report deals with similar bodies observed in mammary tumors of C3H/Crg l mice following treatment with large amounts of cortisol acetate. Bernhard, Bauer, Gu~rin, and Oberling (1955) indicated that the inclusion bodies were microscopically visible aggregates of the virus-like particles seen with the electron microscope. Porter and Thompson 0948) first demonstrated such particles associated with mouse mammary tumors; since then they have been seen by a number of investigators (cf. Bernhard, 1958; Dmochowski, 1960). These particles are spherical double membranes averaging 700 A in diameter (A particles), clustered within the apical cytoplasm. B particles, about 1100 A in diameter and of a more complex structure, occur in lumina and occasionally intracellularly (Pitelka, Bern, DeOme, Schooley, and Wellings, 1958). They are found not only in mammary tumors, but also in large numbers in hyperplastic alveolar nodules, and infrequently in normal tissues. An abundance of these particles appears to be diagnostic of hyperplasias with preneoplastic significance (Pitelka, DeOme, and Bern, 1960).