Breast Cancer Laterality and Molecular Subtype Likely Share a Common Risk Factor

Abstract

Background: To investigate the epidemiologic features of breast cancer laterality and molecular subtypes in Southern China, we retrospectively analyzed the clinical data of patients with a definite diagnosis of breast cancer in 2013-2017. Methods: Data for inpatient hospitalization associated with breast cancer were obtained from the Affiliated Hospital of Guangdong Medical University, Guangdong Province, South China. Around 2060 cases who were diagnosed with unilateral breast cancer for the past 5 years were classified based on laterality and molecular subtypes. Molecular subtypes were defined in accordance with the 2013 St. Gallen recommendations. All statistical analyses were performed using Statistical Product and Service Solutions version 21 and Excel version 2010. Results: Breast cancer is more likely to be diagnosed in the left breast than in the right by around 5%. In both in situ and invasive carcinomas, the right breast is more commonly affected than the left in young (<40 years old) patients, whereas the opposite is true for old (≥40 years old) patients. Except for invasive mucinous and invasive medullary breast cancers, other histological types occur more on the left side than on the right. The mean age at diagnosis ranges from 47.6 years for women with luminal B(HER-2 ) tumors to 51.8 years for women with HER-2-overexpressing tumors. In situ cancer is likely to be diagnosed with luminal B(HER-2-). Except for invasive medullary and invasive not specified cancers, other invasive carcinomas are also most likely to be diagnosed as luminal B(HER-2-. The age of ≥40 years is a risk factor for luminal B(HER-2), and a significant correlation is present between the left breast and luminal B(HER-2 ). Conclusion: We explored the risk factors of breast cancer laterality and molecular subtypes and found that age may be a predictor of breast cancer laterality. In the study of molecular subtypes of breast cancer, we analyzed the risk factors of various molecular subtypes. We found that age and laterality are probable risk factors of the luminal B(HER-2 ) type of breast cancer. These results provide a basis for the epidemiological characterization of breast cancer. Funding: Supported by Major application special topics of the science and technology department of Guangdong province, China (No. 2015B010131016) and Science and Technology Planning Project of Guangdong Province, China (No. 2014A020212291). Conflict of interest: No conflict of interest exits in the submission of this manuscript. Ethical approval statement: This research was approved by the Medical Sciences Ethics Committee of the Affiliated Hospital of Guangdong Medical University. All study participants received detailed written information in advance and signed a written informed consent prior to the study. Results of the study will be published as well.