Keytruda for High TMB in ER+ Metastatic Breast Cancer — Anyone With Experience?
My wife has ER-positive, HER2-low (IHC 1+) metastatic breast cancer and has been living with metastatic disease for about 10 years.
Unfortunately, her latest PET scan has shown progression after approximately three months on Xeloda. Her oncologist is now considering Keytruda (pembrolizumab) because of high tumor mutational burden.
Her molecular results include:
• Tissue TMB: approximately 16 mut/Mb
• More recent blood TMB: approximately 65 mut/Mb
• MSS
• PD-L1 CPS 1
I understand that Keytruda is not routinely used for most ER-positive breast cancers, but high TMB provides a potential rationale for immunotherapy. We are discussing this carefully with her oncologists and are also seeking second opinions.
I would really appreciate hearing from anyone with ER-positive metastatic breast cancer who received Keytruda because of high TMB.
If you are comfortable sharing, what was your TMB? Did you have tumor shrinkage or stable disease? How soon was the first scan, and how long did the response or disease control last? I would also be interested in how well you tolerated the treatment.
Enhertu remains another option for my wife because she is HER2-low, but at present I am particularly trying to learn about real-world experiences with Keytruda in high-TMB ER-positive breast cancer.
Thank you very much to anyone willing to share their experience.