Quantitative Assessment of Mammary Gland Density in Rodents Using Digital Image Analysis

Parallel to mammographic analysis in humans, measurements of rodent mammary gland density were derived from area-based or volume-based algorithms and included: total circumscribed mammary fat pad mass, mammary epithelial mass, and epithelium-free fat pad mass. These values permitted estimation of absolute mass of mammary epithelium as well as breast density. The biological plausibility of these measurements was evaluated in mammary whole mounts from rats and mice. During mammary gland development, absolute epithelial mass increased linearly without significant changes in mammographic density. Treatment of rodents with tamoxifen, 9-cis-retinoic acid, or ovariectomy, and occurrence of diet induced obesity decreased both absolute epithelial mass and mammographic density. The area and volumetric methods gave similar results.Digital image analysis can be used for screening agents for potential impact on reproductive toxicity or carcinogenesis as well as for mechanistic studies, particularly for cumulative effects on mammary epithelial mass as well as translational studies of mechanisms that explain the relationship between epithelial mass and cancer risk.Rodent models have been used extensively to study mammary gland development and for investigations of many aspects of reproductive toxicology and breast carcinogenesis [1,2]. Mammary gland development occurs postnatally and is affected by initiation of ovarian function as occurs in humans at the time of menarche [3]. The development of the rodent mammary gland has been described in detail [3-5]. However, while representative images of mammary gland gross morphology are frequently reported in the literature, the actual quantification of changes in gross morphology is uncommon and rarely have such analyses been extended to the entire mammary gland rather than a small representative area. The work reported herein describes a technique for automated collection of digital images of rodent mammary glands excised as a mammary g