Fluorescence in situ hybridisation analysis of human epidermal growth factor receptor 2 status for breast cancer cases in Brunei Darussalam

Background Breast cancer is one of the leading cancers among females of Brunei Darussalam. There are four subtypes of breast cancer, including human epidermal growth factor receptor 2 (HER‐2) positive breast cancer, which is known to be more aggressive and have a poor prognosis. Aim This study aims to assess the proportion of HER‐2 positive cases and the association of HER‐2 positivity with patients' epidemiological and clinicopathological factors in Brunei Darussalam. Methods and results A total of 146 breast cancer cases that were sent for fluorescence in situ hybridisation (FISH) analysis from 1 January 2012 to 31 December 2016 were obtained from The Brunei Cancer Centre, Brunei Darussalam. Data analysis was done with regards to age at diagnosis, ethnicity, stage at diagnosis and HER‐2 results by immunohistochemistry (IHC) and FISH. Majority of the study population were diagnosed before the age of 50 years and the median age was 52.0 years. 58.2% (n = 85) cases were reported as IHC 3+, followed by 23.3% (n = 34) IHC 2+ cases and 18.5% (n = 27) negative cases. The proportion of true HER‐2 positive cases in total by FISH analysis was 34.9% (n = 51). Majority of Stage IV HER‐2 positive cases had metastases to the liver or bones. Conclusions Age at diagnosis is significant in determining HER‐2 status of tumours by FISH (P = .045). Tumour size (P