I had sbrt for 1 bone met, and ihc from it was Er50Pr0, Her2 negative. Initial ihc was Er90Pr30 adter surgery. Im...

I understand your concern about the change in ER expression levels and its potential impact on endocrine therapy effectiveness. Let me provide some evidence-based information:

According to NCCN Breast Cancer Guidelines (2023):

• Changes in receptor status (like ER levels) between primary and metastatic sites can occur in 10-40% of cases
• Retesting of metastatic sites is recommended precisely because of these potential changes
• The guidelines still recommend continuing endocrine therapy even with decreased ER expression, as long as it remains positive (≥1%)

The American Society of Clinical Oncology (ASCO) Guidelines state that:

• Several approaches may help optimize endocrine therapy response:

1. Adding CDK4/6 inhibitors to endocrine therapy
2. Using different classes of endocrine therapy (switching between aromatase inhibitors, fulvestrant, or tamoxifen)
3. Considering clinical trials testing novel combinations

According to ESMO Guidelines:

• Epigenetic modifications can contribute to reduced ER expression
• Some clinical trials are investigating drugs called "epigenetic modifiers" that might help restore ER expression
• DNA methyltransferase inhibitors and histone deacetylase inhibitors are being studied for this purpose

Important recommendations:

1. Discuss these findings with your oncologist to determine the best treatment strategy
2. Consider genomic testing if not already done to identify potential targeted therapy options
3. Ask about clinical trials investigating treatments for reduced ER expression

Remember: While ER expression has decreased, 50% is still considered positive and endocrine therapy can still be beneficial. Your oncologist can help determine the optimal approach based on your specific situation.