750 - HER2 positive rates in Invasive Lobular Breast Carcinoma : A study amongst 1,095 consecutive Asian patients

Background

Infiltrating lobular carcinoma (ILC) represents about 10% of breast cancer and rarely shows over-expression of human epidermal growth factor receptor 2 (HER2). This study aims to investigate the prevalence of HER2 positive (HER2+) ILC patients in Singapore and their clinical characteristics.

Methods

A retrospective review of female ILC patients seen between January 1985 and March 2018 at National Cancer Centre Singapore (NCCS) was conducted. Demographic and clinical data was collected from medical records. HER2+ ILC was defined as a score of 3+ on immunohistochemistry (IHC) or an IHC score of 2+ and a HER2/CEP17 ratio ≥2.0 for samples after 1 January 2014 and HER2/CEP17 ratio ≥2.2 for samples before 1 January 2014 on fluorescence in situ hybridization (FISH) testing. Clinical characteristics were evaluated in relation to HER2 status.

Results

A total of 1095 patients (mean age at diagnosis 55.3 years) were included; 784 Chinese (71.6%), 90 Malay (8.2%) and 77 Indian (7.0%). Distribution of ILCs by stage were: 282 Stage 1 (28.8%), 369 Stage 2 (37.7%), 247 Stage 3 (25.2%) and 67 Stage 4 (6.8%). Mean tumour size was 3.1cm (range 0 - 14.5cm), 112 of 858 patients with known tumour grade were grade 3 (13.1%) and 890 of 975 patients with known estrogen receptor (ER) status were ER + (91.3%). Prevalence of HER2+ ILC was 10.8% (100 of 929 patients with known HER2 status). HER2+ status was significantly associated with higher tumour grade (24 Grade 3 [24.0%], p < 0.001) and ER negativity (24 ER + [24.0%], p = <0.001) but not higher stage (29 Stage 3 [29.0%] and 9 Stage 4 (9.0%), p = 0.196).

Conclusions

Compared to reported HER2+ rates of 1-6% in previous ILC case series, 10.8% of patients in our large retrospective cohort were HER2+. HER2+ ILC were more likely to be ER negative and of higher tumour grade. Further studies are warranted to explore the biology and molecular characteristics of HER2+ ILC in Asian patients.

Editorial acknowledgement

Clinical trial identification

Legal entity responsible for the study

National Cancer Centre Singapore.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.