Advance Publication Acta Histochem. Cytochem. 40 (2): 61–67, 2007 doi:10.1267/ahc.07008 J01TRAa03oecHp.4kgt1aaC47yu2n-0olH65aS7,7r98io0Js/90Aatc0o10phi8recacttihn.yc0el7meo0fi0cH8aisetoCchyetomcihsetrmyiacnad Cytochemistry Promoting Effects of Milk on the Development of 7,12-dimethylbenz(a)anthracene (DMBA)-induced Mammary Tumors in Rats De-Fu Ma1,2, Ryohei Katoh2, Hong Zhou1 and Pei-Yu Wang1 1Department of Social Medicine & Health Education, School of Public Health, Peking University, Beijing, 100083, China and 2Department of Human Pathology, University of Yamanashi Interdisciplinary Graduate School of Medicine and Engineering, Yamanashi 409–3898, Japan 00 Received February 19, 2007; accepted March 20, 2007; published online May 10, 2007 CopyrTigoht a©ss2e00s7s AtHheC effect of milk on the development of 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary tumors, 48 female Sprague-Dawley rats treated with DMBA were divided into 3 groups and given 1 of 3 test solutions for 20 weeks as their drinking liquid: milk, estrone sulfate solution or tap water. The milk group showed a significantly great incidence (75%) in tumor development compared with the water group (38%) and was com- parable to the estrone sulfate group (69%). Mean tumor number per rat in the milk group was significantly higher than that in the water group (p=0.009). We classified the mammary tumors into three histological types: intraductal papilloma, fibroadenoma, and adenocarci- noma. Although the percent of intraductal papilloma and fibroadenoma was almost same among the three groups, malignant tumor was found only in the milk and estrone sulfate groups. In conclusion, our results indicate that milk as well as estrone sulfate promotes the development of DMBA-induced mammary tumors in rat and could be associated with the occurrence of adenocarcinoma. Key words: mammary tumor, milk, smooth muscle actin, proliferating cell nuclear antigen, estrogen receptor I. Introduction Breast cancer is the most common malignant neoplasm, and is the number one cause of cancer-related deaths in nonsmoking women [3]. The incidence of breast cancer has been increasing in both developed and developing countries [4]. Although epidemiological studies have identified vari- ous risk factors, including obesity, menarche at young age, and late menopause, these known risk factors seem to ac- count for only a third of the breast cancer cases [10, 23]. Recently, an epidemiological analysis revealed that the in- cidence of breast cancer in 42 countries is highly correlated (r=0.79) with the consumption of milk and dairy products Correspondence to: Ryohei Katoh, Department of Human Pathology, University of Yamanashi Interdisciplinary Graduate School of Medicine and Engineering, 1110 Shimokato, Chuo, Yamanashi 409–3898, Japan. E-mail: rkatoh@yamanashi.ac.jp Pei-Yu Wang, Department of Social Medicine & Health Education, School of Public Health, Peking University, Beijing, 100083, China. E-mail: wpeiyu@bjmu.edu.cn [22]. The positive association between milk and breast can- cer has been proved by some case-control studies and cohort studies [18, 26]. Recently, Qin et al. reported that low-fat milk pro- moted the development of 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary tumors in rats [17]. But they did not thoroughly observe their natural history and mor- phology, or perform pathological classification for experi- mental tumors to assess the effects of milk on morphology and pathology of tumors. It is possible to evaluate tumori- genic response by palpable tumors, but the true nature of palpable lesions can be determined only through histo- logical examination [21]. Moreover, the classification of tumors is very useful for the further interpretation of ex- perimental data [21]. In the present study, we performed haematoxylin-eosin staining (HE) and carefully implement- ed pathological classification for all experimental tumors. Since the presence of myoepithelial cells is commonly regarded as the hallmark of benignity for human tumors [2, 14] and proliferating cell nuclear antigen (PCNA) is sensi- © 2007 The Japan Society of Histochemistry and Cytochemistry