From Arimidex to Tamoxifen

Hi;  Thank you for taking the time to review my question.  A quick background:

1. I started chemo treatment (ACT) in June 2008, and at that time I stopped having my periods.  
2. After chemo ended in Nov. 2008, I was put on Arimidex because my blood tests showed that I was POST-menopause.  
3. However, just a few days ago, surprisingly I started having my periods again (9 months after finishing chemo!).  
4. My Surgical Pathology Report shows "Estrogen: Positive > 75% tumor ___ staining"

So, now that I'm back to being PRE-menopausal, I assume that my oncologist is going to recommend Tamoxifen. So, my questions are:
Q1. What are the risks of going from Arimidex to Tamoxifen?
Q2. What is the best way for me to discuss with him about the benefits vs. risks of taking Tamoxifen?
Q3. Should I wait a while (how long?) before I start taking Tamoxifen?
Q4. Does the fact that I went from POST-menopause back to PRE-menopause give any additional indication regarding my risk for recurrence, etc.?

Thanks! -Krista

[Cleveland Clinic]

Dear Krista, Tamoxifen and Arimidex work in different ways to block estrogen.  Tamoxifen binds to estrogen receptor sites on cancer cells thus blocking estrogen from going into the cancer cell.  This interferes with cell growth and eventually leads to cell death.  Arimidex is an aromatase inhibitor.  This means it blocks the enzyme aromatase (found in the body's muscle, skin, breast and fat), which is used to convert androgens (hormones produced by the adrenal glands) into estrogen.   In pre-menopausal women there is more circulating estrogen so arimidex would not adequately limit estrogen, this is why it is not used in pre- menopausal women.     One of the first things that would want to be established is your menopausal status.  The decision to switch to Tamoxifen from Arimidex would need to be put into context of your particular situation and would be best discussed with your oncologist.