25P - Clinical presentations and prognostication of HER2-low breast cancer in Taiwan

Background

With the advent of novel antibody-drug conjugate (ADC), an emerging subgroup of human epidermal growth factor receptor 2 (HER2)-low breast cancer has been recognized which may take advantage from the anti-tumor activity. We took advantage of Taiwan Cancer Registry (TCR) to evaluate the clinical presentations and prognostication for HER2-low breast cancer.

Methods

HER2-low breast cancers were defined operationally with HER2 immunohistochemistry (IHC) 1+ or 2+ with a negative fluorescence in situ hybridization (FISH) while HER2-zero defined with an IHC score 0. Breast cancer index cases (n=189465) from TCR between 2007 and 2017 were reduced to 133546 sides of breast cancer per subject. Clinical features such as IHC test, stage, grade and outcomes such as relapse-free and overall survival were compared between HER2-low and HER2-zero.

Results

The safety analysis group comprised 37195 HER2-negative breast cancers, including 14288 IHC 1+, 10486 FISH-negative, 8907 IHC 0 and 3323 IHC 2+/FISH-undetermined cases. Among HER2-negative breast cancers, the proportion of HER2-low and HER2-zero was 68.9% and 31.1%, respectively, after excluding HER2 ambiguity. Overall survival was 95.7% versus 95.9% for HER2-low and HER2-zero breast cancers, which was 94.1% and 94.7% for relapse-free survival. The distributions of pathological stages from 0 to IV were 6.7%, 41.5%, 38.5%, 13.1% and 0.3% for HER2-low and were 8.5%, 42.8%, 37.5%, 11% and 0.4% for HER2-zero breast cancers. Regarding estrogen receptor (ER) and progesterone receptor (PR) status, 87.6% and 80.9% of the HER2-low cases were ER+ and PR+ while 81.9% and 74.8% of the HER2-zero patients were ER+ and PR+. High or poorly differentiated grade was reported from 23.4% of HER2-low and 25.5% of HER2-zero breast cancers. The diagnosed age was 54 versus 54.3 between HER2-low and HER2-zero breast cancers (P=0.02).

Conclusions

HER2-low status is not a prognostic marker for Taiwanese breast cancers while a slightly younger age of disease onset, less than half diagnosed with stage 0 and I, more ER and PR positivity and fewer grade III disease were observed for HER2-low phenotype compared with HER2-zero counterpart. These trivial differences distinguished HER2-low from HER2-zero spectrum among Taiwanese HER2-negative breast cancers.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

LMT.

Funding

Melissa Lee Cancer Foundation.

Disclosure

All authors have declared no conflicts of interest.