Clinical Outcomes of CDK4/6 Inhibitor Therapy in HR+/HER2- Metastatic Breast Cancer: A Multicenter Comparison of HER2-Low and HER2-Zero Subgroups.

Although treatment response according to HER2 expression level has not been clearly established in the literature, most studies have reported a slight trend toward longer PFS in HER2-zero patients [ 12 , 20 – 27 ].

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However, these differences did not reach statistical significance and should be interpreted as nonsignificant numerical variations.

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