Integumentary System
Mammary Gland - Fibrosis
Narrative
Comment:
Variable degrees of fibrosis of the mammary gland lobule are commonly seen in older rats and mice. Mammary gland fibrosis is usually periductular and often occurs secondary to other changes, such as cystic ductal dilation, galactoceles, chronic inflammation, atrophy, epithelial hyperplasia, and neoplasia. However, mammary gland fibrosis can also be a primary change due to experimental manipulations or chemical exposures, such as implantation of foreign materials, iodine deficiency, or prenatal exposure to organochlorines in rats. It can also be associated with the proliferation of small- and medium-sized ducts in BALB/c mice treated with epidermal growth factor. Mammary gland fibrosis is characterized by increased amounts of mature fibrous connective tissue surrounding mammary gland ducts (periductular) and extending into the adjacent mammary adipose tissue (Figure 1and Figure 2). Diffuse sheets of mature fibrous connective tissue are a feature of lobular hyperplasia (Figure 3 and Figure 4). Fibrosis must be differentiated from early fibroadenomas, which are nodular, space-occupying lesions.
Recommendations:
Mammary gland fibrosis should be diagnosed and assigned a severity grade if it is a primary change. Fibrosis occurring as a secondary change to other lesions (such as duct dilatation, galactocele, inflammation, epithelial hyperplasia, neoplasia, etc.) should not be diagnosed separately unless warranted by severity, though it should be described in the pathology narrative.
References:
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| El Sheikh Saad H, Meduri G, Phrakonkham P, Berges R, Vacher S, Djallali M, Auger J, Canivenc-Lavier MC, Perrot-Applanat M. 2011. Abnormal peripubertal development of the rat mammary gland following exposure in utero and during lactation to a mixture of genistein and the food contaminant vinclozolin. Repro Toxicol 32(1):15-25. |
| Eskin BA, Grotkowski CE, Connolly CP, Ghent WR. 1995. Different tissue responses for iodine and iodide in rat thyroid and mammary glands. Biol Trace Element Res 49(1):9-19. |
| Foster WG, Younglai EV, Boutross-Tadross O, Hughes CL, Wade MG. 2004. Mammary gland morphology in Sprague-Dawley rats following treatment with an organochlorine mixture in utero and neonatal genistein. Toxicol Sci 77(1):91-100. |
| Greaves P. 2007. Mammary gland. Histopathology of preclinical toxicity studies. Interpretation and relevance in drug safety evaluation, 3rd ed. Academic Press pp. 68-98. |
McMartin DL, Sahota PS, Gunson DE, Han Hsu H, Spaet RH. 1992. Neoplasms and related proliferative lesions in control Sprague-Dawley rats from carcinogenicity studies. Historical data and diagnostic considerations. Toxicol Pathol 20:212-225.
Abstract: https://www.ncbi.nlm.nih.gov/pubmed/1475582| Molinolo A, Simian M, Vanzulli S, Pazos P, Lamb C, Montecchia F, Lanari C. 1998. Involvement of EGF in medroxyprogesterone acetate (MPA)-induced mammary gland hyperplasia and its role in MPA-induced mammary tumors in BALB/c mice. Cancer Lett 126(1): 49-57. |
Seely JC, Boorman GA. 1999. Mammary gland and specialized sebaceous glands. In: Pathology of the Mouse: Reference and Atlas (Maronpot RR, Boorman GA, Gaul BW, eds). Cache River Press, Vienna, IL, 613-635.
Van Zwieten MJ, HogenEsch H, Majka JA, Boorman GA. Nonneoplastic and neoplastic lesions of the mammary gland. In: Mohr U, Dungworth DL, Capen CC (eds.). 1994. Pathobiology of the aging rat, Vol. 2. International Life Sciences Press pp. 459-474.
Mammary gland - Fibrosis in a male F344/N rat from a chronic study. Mammary gland fibrosis is characterized by increased amounts of mature fibrous connective tissue both surrounding mammary gland ducts and extending into the adjacent mammary adipose tissue (arrows).
All Images
Mammary gland - Fibrosis in a male F344/N rat from a chronic study. Mammary gland fibrosis is characterized by increased amounts of mature fibrous connective tissue both surrounding mammary gland ducts and extending into the adjacent mammary adipose tissue (arrows).
Mammary gland - Fibrosis in a male F344/N rat from a chronic study (higher magnification of Figure 1). Mature fibrous connective tissue surrounds a mammary gland duct and alveoli and extends into the adjacent mammary adipose tissue.
Mammary gland - Fibrosis in a female F344/N rat from a chronic study. Diffuse sheets of mature fibrous connective tissue are a feature of concurrent lobular hyperplasia in the mammary gland.
Mammary gland - Fibrosis in a female F344/N rat from a chronic study (higher magnification of Figure 3). A diffuse sheet of mature fibrous connective tissue surrounds mammary gland ducts and alveoli.