<p>Breast cancer became the most prevalent malignancy among women, and HER2 expression status is critical for treatment decisions. With the emergence of ADC drugs, HER2 low-expressing patients who previously did not respond well to traditional anti-HER2 therapies may now benefit. In this study, immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) were applied to assess HER2 expression in 349 patients with HER2-non-positive breast cancer. Our analysis revealed that HER2-low tumors exhibited fewer grade III tumors (39.74% and 55.65%, respectively, <i>P</i> = 0.005) and higher positivity for estrogen receptor (ER, 88.89% vs. 61.74%, <i>P</i> &lt; 0.001) and progesterone receptor (PR, 84.62% vs. 57.39%, <i>P</i> &lt; 0.001) compared to HER2-ZERO tumors. Of the 349 cases, IHC was ultimately evaluated in 327, the antibodies demonstrated only 64.22% (95% CI: 58.76–69.42%) agreement between clone 4B5 and clone EP3. Pathologist 1, who had more extensive working experience, demonstrated higher consistency (94.19%) with the gold standard when using clone EP3, compared to Pathologist 2 (74.31%). FISH analysis revealed significant differences in HER2/CEP17 ratio and average HER2 copy numbers between HER2-ZERO and HER2-low tumors, but no clear cut-off value could be identified. Notably, HER2/CEP17 ratio mostly between 1 and 2, with HER2-ZERO tumors primarily ≤ 1.4, and average HER2 copy numbers were mostly ≥ 2 and &lt; 4, with HER2-ZERO tumors primarily ≤ 2.5. Despite distinct clinicopathological features, FISH remains inadequate for distinguishing HER2-low from HER2-ZERO expression. Further studies are needed to improve HER2 assessment in this challenging subset of patients.</p>

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Exploring the heterogeneity of HER2 gene status and expression in non-positive breast cancer patients: insights from immunohistochemistry and fluorescence in situ hybridization

  • Jingmin Zhong,
  • Beibei Gao,
  • Qingjie Wang,
  • Jun He,
  • Danjv Luo,
  • Chen Zhang,
  • Jun Fan,
  • Xiu Nie

摘要

Breast cancer became the most prevalent malignancy among women, and HER2 expression status is critical for treatment decisions. With the emergence of ADC drugs, HER2 low-expressing patients who previously did not respond well to traditional anti-HER2 therapies may now benefit. In this study, immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) were applied to assess HER2 expression in 349 patients with HER2-non-positive breast cancer. Our analysis revealed that HER2-low tumors exhibited fewer grade III tumors (39.74% and 55.65%, respectively, P = 0.005) and higher positivity for estrogen receptor (ER, 88.89% vs. 61.74%, P < 0.001) and progesterone receptor (PR, 84.62% vs. 57.39%, P < 0.001) compared to HER2-ZERO tumors. Of the 349 cases, IHC was ultimately evaluated in 327, the antibodies demonstrated only 64.22% (95% CI: 58.76–69.42%) agreement between clone 4B5 and clone EP3. Pathologist 1, who had more extensive working experience, demonstrated higher consistency (94.19%) with the gold standard when using clone EP3, compared to Pathologist 2 (74.31%). FISH analysis revealed significant differences in HER2/CEP17 ratio and average HER2 copy numbers between HER2-ZERO and HER2-low tumors, but no clear cut-off value could be identified. Notably, HER2/CEP17 ratio mostly between 1 and 2, with HER2-ZERO tumors primarily ≤ 1.4, and average HER2 copy numbers were mostly ≥ 2 and < 4, with HER2-ZERO tumors primarily ≤ 2.5. Despite distinct clinicopathological features, FISH remains inadequate for distinguishing HER2-low from HER2-ZERO expression. Further studies are needed to improve HER2 assessment in this challenging subset of patients.