Nali A. Maaruf*, Suhail M. Najjar and Salah A. Ali

Breast carcinoma is the second most common type of cancer in women, and its progress and outcome depend on the expression of the human epidermal growth factor receptor 2 (HER2), progesterone receptor (PR), estrogen receptor (ER), and Ki67 genes. This research evaluated morphological, histological, and immunohistochemical markers, including ER, PR, Ki67 and HER2 expression differences between right and left mammary tumors. Two hundred, 7-week-old virgin female Sprague Dawley rats, weighing 100–120g were used in the study. The rats were divided into two groups: G1 = control negative (n = 50), which received just a placebo (normal saline), and G2 = control positive (n = 150), which received a single dose of 20 mg/kg body weight of DMBA by gavage after being dissolved in sesamoid oil. Animals were weighed and monitored weekly until the end of the study. On week 16, a lumPwas taken from the right and left mammary glands and examined by hematoxylin-eosin staining and immunohistochemistry (IHC) using ER, PR, HER2 and Ki67 antibodies. Out of the 150 total numbers, 87 tumors were induced by DMBA; 44.83% (39/150) appeared on the right mammary gland chain and 49.43% (43/150) on the left, and most of the tumors were found on cervical-thoracic glands. ER, PR and Ki67 expression were higher than HER2 in all tumors. We found that the histopathological features of mammary cancer in rats induced by DMBA were similar to those of human breast cancers in terms of location, histopathologic alterations, and IHC markers, and location plays a significant role in tumor development and IHC susceptibility.