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My oncologist said I may only get a 1-3% benefit on tamoxifen so it may not be worth the side effects. How do I decide this?

A MyBCTeam Member asked a question 💭
Saskatchewan

I’m 54 but have gotten heavy periods since quitting birth control a few months ago when I found out I have ER/PR positive breast cancer. My levels have increased greatly off the pill to Estradiol (E2) 1,635 pmol/L (from 88)
FSH 13.40 IU/L
LH 36.7 IU/L. I feel that quitting the Mirvala birth control pill was a mistake and now I have high levels that are feeding cancer. I also am waiting on a thick uterine lining (21 cm) biopsy. I’ve finished lumpectomy and radiation previously

October 30
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A MyBCTeam Member

Uterine thickening along with heavy bleeding can be a sign of endometrial cancer and endometrial cancer is a side effect of Tamoxifen. Endometrial cancer, like breast cancer, can also be hormone positive. I was diagnosed with HR+ breast cancer in 2017 and the with HR+ endometrial cancer in 2019. I had a hysterectomy and they took out the uterus, fallopian tubes, and ovaries. I was 53 at the time and hadn't yet entered menopause. The AIs are supposed to do a better job of reducing hormone levels than the tamoxifen, but you have to be in menopause. You should be nearing menopause so it may be worthwhile to suppress ovarian function with medication or have your ovaries removed and take an AI instead of the Tamoxifen.

6 days ago (edited)
A MyBCTeam Member

@A MyBCTeam Member

Your doctor would not go ahead with the tamoxifen right now immediately where you are waiting for a biopsy regarding your uterine lining thickening as the tamoxifen could further thicken the lining.

That would be an illogical move on the Dr’s part.

The doctors in tandem need to figure out what is the best possible care for you.

The uterine thickening is a side effect for some women already on Tamoxifen.

7 days ago
A MyBCTeam Member

My experience as a man on Tamoxifen could be different. I have had no ill effects. I would suggest you take it and see how the side effects are. Not everyone has the same ones. You are the only one that can decide if they are bearable. Good luck.

7 days ago
MyBCTeam

This is genuinely a complex situation with several things happening at once — it makes sense that you're trying to piece it all together. The decision about tamoxifen when the projected benefit is small is deeply personal, and it really comes down to weighing that benefit against your individual side effect burden and Show Full Answer

This is genuinely a complex situation with several things happening at once — it makes sense that you're trying to piece it all together. The decision about tamoxifen when the projected benefit is small is deeply personal, and it really comes down to weighing that benefit against your individual side effect burden and overall health picture.

For ER/PR positive breast cancer, tamoxifen works by blocking estrogen from fueling cancer cell growth. Even a 1–3% absolute benefit may feel meaningful to some people and less so to others — there's no universally "right" answer here. Your concern about rising estrogen levels is understandable. With ER/PR positive breast cancer, high circulating estrogen is worth discussing urgently with your oncologist and gynecologist together, especially given your heavy periods and the thick uterine lining awaiting biopsy.

Importantly, tamoxifen is already linked to uterine lining changes, including thickening and polyps. Your biopsy results will be very important information before making any tamoxifen decision. Some key things worth raising with your care team:

- Whether your hormone levels post-pill need to be managed before or alongside any hormonal therapy decision
- Your biopsy results — these could directly affect whether tamoxifen is appropriate for you
- Alternative hormonal therapies — depending on your menopausal status, other options may exist
- The risk of stopping tamoxifen early if you do start — research shows stopping early can significantly increase recurrence risk Please don't make any changes to medications on your own right now. With your biopsy pending and hormone levels in flux, this is a moment where having your oncologist and gynecologist aligned on a plan is really important. You're asking exactly the right questions — bring all of this to your next appointment.

October 30

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