Women applications of a comparative bilateral female rats’ breast carcinoma findings
Authors: Najjar Suhel , Maaruf Nali , A. Ali Salah 
Published: February 2025

Background and objective: Breast carcinoma is the second most common type of cancer in women, and its incidences and consequences depend on internal congenital factors and various environmental chromosomal mutational factors. Multiple studies had evident heterogeneity in ipsilateral and contralateral breast cancers, of these the higher incidence of left breast cancer than right for indistinct reasons. This review article is concerned with the possibility of gathering the results of a recent research in comparison of bilateral rats' mammary cancer as a clue in evaluating the variations of the women’s right and left breast tumors. Bilateral breast's gross, microscopical consistency and the pathological, immunohistochemical expressions of both sides of breast tumors were studied, hoping to explain the disparity in bilateral breast cancer incidence and may exploit it for prophylactic purposes.

Material and methods:The study used two hundred virgin female Sprague Dawley rats aged 7 weeks, weighing 100–120g. The rats were divided into two groups: 50 rats used as a control group, which received a placebo, and 150 rats carcinogenic exposed group, which received a single oral dose of (7.12-Dimsthylbenz [a]anthracene (DMBA). Animals were weighed and monitored weekly until the end of the study. The lumps bilaterally appeared after induction and were excised for gross structural, histological, and immunohistochemical examinations. The study was also supplemented by normal women's bilateral mammography computerized technique (MATLAB) software analysis for gross anatomical study, as this was impossible in rats. Statistics data groups were analyzed using SPSS version 22.

Results: Among (150) rats exposed to DMBA, only (87) developed tumors as first noticed after (13-16) weeks. Tumors were distributed as 43.68% (38/87) on the right breasts, and 56.32% (49/87) on the left, including (5/87) bilateral, moreover to (11) right breast’s fibroadenoma. The weight and size of the tumors were greater on the right than left. Histopathological features of rat’s mammary cancer induced by DMBA were similar to those of human breast cancers regarding location, and histopathologic modifications, such as ductal carcinoma in situ, Invasive ductal carcinoma, lobular carcinoma in situ, and invasive lobular carcinoma. On the right side, Lobular carcinoma was observed tightly packed in clusters forming thin strands of cells arranged in a linear design (Indian file) with abundant eosinophilic infiltration, while on the left side carcinoma were disseminated irregularly in dense fibrous tissue and fat with less or damaged eosinophilic infiltrations.

The immunohistochemistry scores matched the tumor growth, susceptibility, and type. Estrogen receptors, progesterone receptors, and Kiel clone 67 (Ki67) expressions were higher with invasive ductal carcinoma. The invasive lobular carcinoma was negative for Human Epidermal Growth Factor Receptor 2 (HER2) and KI67. No triple-negative results were observed. The results of the women’s supplementary study by mammography analysis revealed that the majority of Iraqi females were heterogenous type III, and the left breast was denser than the right.

Conclusion: Among 150 rats only 58% developed various breast tumors after a single dose of carcinogens. The lower incidence of right breast carcinoma than the left is supposed to be due to the lower density, more fatty tissues, and lower immunity of the left breast. The left breast carcinomas were multifocal while the right breast carcinomas were localized in a single sector but characterized by a more aggressive cellular multiplication. Accordingly, if the revealed results are applied to women's breast carcinoma, it may lead to some important hints in understanding some secrets and mapping new management in breast carcinoma in the future.