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ASSESSMENT OF HER2 STATUS IN FEMALE BREAST CANCER: COMPARISON OF FLUORESCENCE IN SITU HYBRIDIZATION AND IMMUNOHISTOCHEMISTRY, IN NATIONAL HOSPITAL ABUJA
Abstract
HER2 positive breast cancers are characterised by over-expression and/or amplification of the
HER2 gene and have a poor prognosis. However, treatment with anti-HER2 antibodies significantly
alters the course of the disease. The most widely accepted methods for assessing HER2 status are
immunohistochemistry (IHC) for protein expression and in situ hybridization (ISH) for detecting
gene amplification. Most centres in this country utilise only IHC in determining HER2 status and
due to its limitations, may result in false negative results. Additionally, there is no alternative test to
re-assess equivocal cases. This study aimed to compare HER2 expression by IHC with HER2 gene
amplification, to determine the clinicopathologic characteristics of breast cancer and correlation
between these and HER2 status. Dual probe (PathVysion HER2 DNA probe kit) FISH was done
assessing the ratio of HER-2/neu and chromosome 17 centromere signal counts. IHC was done
using Novocastra antibody and scored based on ASCO/CAP guidelines. The average age of
diagnosis of breast cancer was 41.8years, the most common histological type was invasive
carcinoma (NST) and majority were intermediate grade tumours. Immunohistochemistry showed
that HER2 +3 tumours accounted for 10%, +2 tumours accounted for 11% and 0/+1 tumours
comprised 79% of breast cancers. The frequency of HER2 amplification was 12%. With FISH,
83% of the IHC +3 cases were amplified and 75% of +2 IHC tumours showed gene amplification.
HER2 positive tumours were seen in younger age but there was no association between HER2
status and tumour grade. This study shows that the frequency of HER2 positive tumours increased
with FISH and a significant percentage of equivocal cases on IHC had gene amplification.
