Correlation between Cancer Breast Subtypes and Age at Presentation in Egyptian Patients; Single Institution Experience

Abstract

Background: Breast cancer is defined according to molecular subtypes. Each molecular subtype defines different disease behavior and requires different treatment. The different molecular subtypes have different risk factors and different distribution across age classes. Aim of the study: To detect the incidence of cancer breast subtypes by age among Egyptian patients treated at the Clinical Oncology Department, Faculty of Medicine, Ain Shams University, in the period between April 2016 and December 2018. Patients and Methods: Inclusion criteria: Cases with proven pathological diagnosis and underwent IHC studies for the molecular subtype while exclusion criteria were: Bilateral cases, cases with unknown molecular subtype or age at presentation, cases with multiple primaries, cases with in situ cancer, male breast cancer cases, and cases diagnosed during pregnancy. Age classes were computed in four groups: from 20 - 35, >35 - 50, >50 - 65 and those older than 65 years of age. Immunohistochemical studies were done; ER, PR and HER2 were recorded for each case, Molecular subtypes were defined as follows: HR+/HER2-, HR+/HER2+, HER2 overexpressed (HER2 positive, HR-) and Triple Negative Breast Cancer; TNBC (HER2 negative, ER negative and PR negative). Results: one thousand and two cases were included in the study. The median age was 51 years and the mean age was 51.64 ± 11.74, with range from 24 to 85 years. The total number of ER positive patients was 706 patients (70.5%), the total number of PR positive patients was 667 (66.6%), and the total number of Her2 positive patients was 286 patients (28.5%). While there were no statistically significant differences in the incidence of ER and PR positivity among all age classes, Her2 over expression decreased with age and the difference was statistically significant (P-value: 0.012). Her2 overexpression subtype incidence decreased by age and it was highest in the younger age group 17.6% compared to 8.2% in the older age group and the difference was statistically significant. Similarly, HR+/HER2- tumors incidence were higher in patients older than 65 (57.4%) and lower in the younger age group (40.5%) (P-value: 0.031). Triple negative tumors incidence ranged from 14.9% for those younger than 35 to 17.2% for those older than 65 years. Conclusion: This study shows that there are significant differences in the age distribution by molecular subtype and the incidence of Her2 overexpression subtype decreases by age. The study also shows that the nature of the breast cancer in the group of Egyptian patients studied is more of the favorable hormonal positive subtype.