HER 2 NEU and BMI 1 gene expression in Invasive Ductal Carcinoma Breast and Its correlation with hormone receptors and other known prognostic factors

INTRODUCTION: Carcinoma of breast is one of the most common human neoplasms both in developed and developing countries accounting for 23% of all the cancers in females.1 There is a steady rise in the incidence of breast cancer worldwide. It is the leading cancer among Asian women. Early detection and advances in treatment have begun to reduce mortality rates. Breast carcinoma exhibits a wide range of morphological phenotypes. The histological appearances of tumor cannot fully reveal the prognosis. Exploration of the molecular pathways of carcinogenesis provides explanation for the different morphologic phenotypes and behavior. A large number of genetic alterations have been identified in breast carcinoma, many of which have potential prognostic and predictive values. Thus estrogen and progesterone receptor expression predict response to tamoxifen therapy and Her2neu over expression predict response to trastuzumab. Recent research in breast biology has provided support for the cancer stem cell hypothesis. Tumor originates from the tissue stem cells through dysregulation of the normally tightly regulated process of self renewal. Cancer stem cells have the potential to self renew and differentiate to generate phenotypically derived cancer cells. The polycomb gene Bmi1 is the critical regulator of self renewal of stem cells and is over expressed in breast cancer. Genomic studies provide a new method of classification of breast cancers based on gene expression patterns. Recently immunohistochemical markers such as ER, PR, Her 2 neu, CK5/6 and EGFR have been used as surrogates for DNA microarray in subtyping breast cancer10. These subtypes predict outcome, patient response to chemotherapy or targeted therapy. Thorough use of molecular techniques like immunohistochemistry and polymerase chain reaction to study the protein and DNA expression profiles may help to predict clinical outcome in individual patients and thus guides to plan personalized therapy. In this study of 60 cases, an attempt is made to assess molecular subtypes of breast cancers and to compare the Bmi 1 gene and Her 2 neu oncoprotein expression with other known prognostic factors. AIMS AND OBJECTIVES: 1. To identify the relative frequency and distribution of breast carcinoma in population. 2. To study the histomorphological features of breast carcinoma including grade, lymph node status, lymphovascular invasion, lymphocytic response, and necrosis. 3. To study the immunohistochemical expression of estrogen and progesterone receptors in invasive ductal carcinoma breast. 4. To study the immunohistochemical expression of Her2neu protein in invasive ductal carcinoma breast. 5. To study the Bmi1 gene expression in invasive ductal carcinoma breast with respect to grading. 6. To determine the correlation of Her2neu and Bmi1 gene expression with hormone receptor status and other known prognostic factors such as tumor size, histological grade, axillary node status, presence of tumor necrosis, lymphocytic response, lymphatic and vascular invasion by tumor. MATERIALS AND METHODS: This study is a retrospective descriptive study of invasive breast cancers conducted in the Institute of Pathology, Madras Medical College and Government Hospital, Chennai during the period between July 2008 and May 2010. Source of data: The invasive ductal carcinoma cases reported in mastectomy specimen received in the Institute of pathology, Madras Medical College between July 2008 to May 2010 from the Department of Surgery, Oncology, Plastic Surgery and Geriatrics, Government General Hospital. A total of 238 mastectomy specimens (simple, modified radical or radical mastectomy) were received during this period. Inclusion Criteria: All the invasive ductal carcinoma cases reported in mastectomy specimens irrespective of the age and sex were included for the study. Exclusion Criteria: • Non neoplastic lesions and benign tumors of breast. • Ductal carcinoma breast reported in incision/excision biopsy and completion mastectomy specimens. • Cases with inadequate material from the tumor for doing both immunohistochemistry and polymerase chain reaction were not included in the study. SUMMARY: 60 breast cancer samples were subjected to immunohistochemistry and polymerase chain reaction to assess the Her2neu and Bmi 1 gene expression and the results were correlated with hormone receptor status and other known clinicopathological prognostic factors. • The relative frequency of breast carcinoma among other surgical cases of Madras Medical College is 2.1%. • The non neoplastic breast lesions form 30.24 %, benign tumors 33.54% and malignant tumors 36.22%. • Breast carcinoma had a peak incidence in the age group of 41 to 50 years. • The most common histological subtype was Invasive ductal carcinoma NOS type which constituted 86.13%. • 52% of the breast cancer presented with T2 size (2 to 5 cm) tumors. • Grade II was the most common grade observed accounting for 52.92%. • Nodal metastasis observed in 52 %. • Lymphatic invasion and vascular invasion were seen in 58% and 22% respectively. • Skin infiltration was seen in 17 % of the tumors. • Lymphocytic infiltration was observed in 65% of the tumors. • Necrosis was found in 52% of the tumors. • Estrogen and progesterone receptor expression was seen in 41% and 51% of the tumors. • Her 2 neu over expression was found in 30 % of the study population. • Immunohistochemical molecular subtyping revealed 45% luminal A type, 12% luminal B subtype, 18% Her 2 type, 7% basal type and 17% unclassified type of tumors. • Her 2 neu over expression showed statistically significant association with high grade tumors and hormone receptor negativity. • No association was found between Her 2 neu expression and menopausal status, size, nodal status, lymphovascular invasion, skin infiltration, lymphocytic infiltration or necrosis. • Higher relative Bmi 1 gene expression was significantly correlated with premenopausal age group, small size tumors, ER negativity, Her 2 neu negativity and luminal A molecular subtype. • No correlation was found between Bmi 1 gene expression and grade, lymph node status, PR status, lymphovascular invasion, skin infiltration, lymphocytic infiltration and necrosis. • Bmi 1 gene expression of this study was not in concordance with the results of the studies conducted in Spain and Netherlands while higher expression was observed in small size tumors similar to the study conducted in Korean population. The variation in expression could be hypothesized as due to many reasons including racial differences between European and Asian population which needs extensive and larger study sample . • Further studies have to be conducted in future to define the clinicopathological importance of Bmi 1 gene expression and the possibility of using this gene as an novel prognostic marker in breast cancer patients. CONCLUSION: The incidence of Invasive ductal carcinoma NOS was higher in this study. Many of our patients presented in younger age with large sized tumors accounting for aggressive nature of breast cancer in our population. Her 2 molecular types were more frequent and Basal type tumors were less frequent in the present study when compared to the western literature. Her 2 overexpression was common with high grade, hormone receptor negative tumors. Higher Bmi 1 gene expression was associated with premenopausal, small size, ER negative, luminal A subtype tumors in concordance to the study conducted in Korean population. Hormone receptor negativity and Her 2 neu overexpression is more common in breast cancers of Indian women than the western population. Due to high prognostic significance, Her 2 neu should be checked in all breast cancer patients so that positive cases can benefit by herceptin therapy and anthracycline based chemotherapy which can improve the survival in these patients. The ethnical difference between European and Asian races may explain the variation in the expression of Bmi1 gene expression. However, further studies have to be conducted in future on a larger number of samples to assess the actual role of Bmi 1 gene expression in Indian population and to explore the possibility of using this gene as a novel prognostic marker in breast cancers.