Tamoxifen for older women (68 years old)

Danaqtr

For my mother, The doctor prescribed tamoxifen for 2 years then another medicine for 3 years. I wonder why tamoxifen for 68 years old? He said it is better for her bones. He said she needs to start it by now before radiation. Is that ok? What are the possible side effects? I read most people got it after radiation but not in same time.

My mother needs knee replacement as well. When she can do it?

She is ER+ 90% HER2 negative, ki67 2%, 2 tumors (1.4 and .8 cm