Changing from Tamoxifen

I had a mastectomy in Nov 06 and a LD recon in 2007. I have been on Tamoxifen for about 18 months now. No real side effects. My onc said that after about two years they will change me on to an aromatase inhibitor. Anyone else done this? Why do they change drugs.

Because cancer has a nasty ability to change and overcome the chemicals used. I have just been taken off tamoxifen and put onto lestrozole as the tamo was no longer holding the situation.

Thanks for your thoughts Phoebe. Thinking of you.