Tamoxifen taking it 10 years after surgery?

hi wondering if anyone is in similar situation? I had cancer 10 years ago & mastectomy. no chemo or radiation. Tamoxifen was discussed as an option. choice was mine as it was considered borderline. I didn't take tamoxifen due to side effects.

Now 10 years on I need iodine mri's as remaining breast tissue is dense. options given are don't worry, 2nd mastectomy or take lower dose of tamoxifen rg 1/2 dose every 2nd day for 3 years. 

Is it unusual to take tamoxifen after 10 years? is it just a knee jerk reaction more for peace of mind? how bad are side effects on the lower dose?

thanks