CLINICAL CHARACTERISTICS OF HER2-LOW BREAST CANCER COMPARED TO HER2-NEGATIVE BREAST CANCER chenghar.yip@gmail.com

3103-09

CLINICAL CHARACTERISTICS OF HER2-LOW BREAST CANCER COMPARED TO HER2-NEGATIVE BREAST CANCER

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Malaysia

Oral or Poster

HER2-low is a newly defined subgroup of breast cancer, defined as tumours with an IHC score of 1+ or 2+ and a negative FISH result. The characteristics of this subgroup are poorly defined, especially in the Asian population, hence the objective of our study is to investigate the relationship between HER2-low breast cancer and its clinical characteristics.

A retrospective cohort study was conducted with Malaysian breast cancer patients. Participants were recruited from a private hospital from 2024 to 2025. Variables collected were HER2 status, age, ethnicity, tumor size, nodal involvement, grade, and hormone receptor status. Differences between continuous variables were examined using the t-test, while differences between the categorical variables were examined using the chi-squared test.

A total of 380 patients were included in this study. Out of the whole study population, 100 (26.3%) were classified as HER2 positive, 197 (51.8%) were classified as HER2 low, while 83 (21.8%) were classified as HER2 negative. A higher proportion of HER2 negative tumors were Grade 3 than HER2 low tumors, at 41.8% vs. 23.8% respectively (p=0.002). A higher proportion of HER2 negative tumors were ER negative compared to HER2 low tumors, at 27.7% vs. 11.7% respectively (p=0.002). This trend also existed for PR status, with 36.1% of HER2 negative tumors negative for PR vs. 20.9% of HER2 low tumors (p=0.012).

HER2-low breast cancers have lower grade and are more likely to be hormone receptor positive than HER2-negative breast cancers, which may indicate a more favorable prognosis.