Rb expression in metastatic ER-positive breast cancer: implications for precision oncology.

Cohort studyBreast cancer research and treatment· Mar 2026

Rb expression in metastatic ER-positive breast cancer: implications for precision oncology.

Doaa Morrar, Dara Ross, Pedram Razavi … Christopher J Schwartz

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Breast & Gynecologic PathologyCohort studyQ1IF 3.5

Rb loss found in 20% of estrogen receptor-positive metastatic breast cancers by immunohistochemistry.

Rb expression in metastatic ER-positive breast cancer: implications for precision oncology.

Doaa Morrar … Christopher J Schwartz

Breast cancer research and treatment · Mar 2026

Purpose

This study aimed to determine the prevalence of Rb loss by immunohistochemistry (immunohistochemistry) in a cohort of estrogen receptor + mBC and to assess its correlation with RB1 genetic inactivation.

Methods

We analyzed Rb immunohistochemistry in 50 consecutive estrogen receptor-positive mBC.

n = 50 consecutive ER-positive mBC

20%

Results

20%

1 in 5 estrogen receptor-positive metastatic tumors lack Rb, risking CDK4/6i resistance

n = 50 consecutive ER-positive mBC

More results

In all evaluable cases (100%, 9/9), Rb loss was associated with p16 positivity.

Neuroendocrine (neuroendocrine) features were observed in 40% (4/10) of mBCs with Rb loss.

MSK-IMPACT data were available for six Rb-deficient cases and revealed pathogenic RB1 alterations in two (33%).

More results

None of the tumors with preserved Rb expression (80%, 40/50) showed RB1 genetic alterations or neuroendocrine features.

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Conclusion · 1 of 2

Rb loss in mBC can be reliably detected by Rb immunohistochemistry, especially when interpreted alongside p16, offering a rapid and cost-effective means of assessing Rb status.

Conclusion · 2 of 2

This approach may identify Rb-deficient tumors that are missed by conventional methods, such as next-generation sequencing, and help guide personalized therapeutic strategies in patients with mBC.

Rb expression in metastatic ER-positive breast cancer: implications for precision oncology.

Rb expression in metastatic ER-positive breast cancer: implications for precision oncology.

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