What is your cut off on ER percent positivity to treat breast cancer as functional triple negative cancer?

I usually use less than 10% ER positivity as the cut off. In this case, I would treat as if the tumor is TNBC.

The answer is dependent on the setting:

• Neoadjuvant (biopsy alone used to determine ER/PR):
  • I sometimes place patients as high as ER 20-30% on KEYNOTE 522. Often, I seek a second opinion on ER/PR IHC in these settings, as I have had cases of false positives at my local institution.
• Adjuvant:
  • I u...