I'll post a question I asked of Dr. Pegram this past Spring:
Are the AI’s apt to stop working over time?
No, in fact right now they’re doing studies of 10 years vs. 5 years because in contrast to Tamoxifen which does apparently sort of “stop working” after 5 years, the AI’s may be a different story. They may continue to work. They work for at least 5 years and now there are big studies looking out to 10. There’s some theoretical rational why longer might actually be better with AIs. There may be a little hint of something that comes out from the longer term studies by next year
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