letrozole and periods

Hello all,

My partner recently switched from Tamoxifen (which she had taken for 5 years) to letrozole. She is 45 and had not had a period since chemo -6 years ago. The oncs had not been certain whether she was properly post menopausal (I’ve posted about this before) - but finally decided that 2 years without a period meant that she could move to Letrozole. This week she has started a bleed which appears to be a period -in that it is accompanied by headached, mood swings (!) etc. She has been to her GP and is being referred back to the onc, though not as an urgent case. Obviously we have a slight concern that the bleeding is something more sinister. She did have a D & C earlier in the year after womb thickening due to Tamoxifen. My gut feeling, though, is that her periods were suppressed by Tamoxifen and, now that is out of her body, they have returned.

I’d be really interested in hearing if anyone else had had the same thing - and, if so, what they did about it - just stop taking Letrozole or have their ovaries suppressed? I guess it would also be useful to hear from anyone who had the same syptoms which turned out to be related to cancer of the womb.



First of all I should point out that I’m not a medic, so obviously your partner must seek medical opinion - but I can talk about my own experience.
Before being diagnosed with Breast Cancer, I too had some post menopausal bleeding, and my Doctor diagnosed a condition known as endometrial hyperplasia (which is where the endometrial lining of the womb continues to thicken). This condition is caused by unopposed oestrogen. What this means is that in post menopausal women the body sometimes continues to produce oestrogen (this production usually occurs in fat cells), which causes the lining to thicken - but the body fails to make the progesterone necessary to counter the oestrogen. As a result, the thickening continues until the woman gets what is called a break through bleed.
Now obviously, you might think this doesn’t apply to your partner, because she is on Tamoxifen - which your post suggests you think stops oestrogen production. But actually this is not the case. Tamoxifen does not stop the body producing oestrogen, it works by disrupting cancers oestrogen uptake. I think maybe you are confusing Tamoxifen with Letrozole/Femera (which does stop oestrogen production by way of inhibiting certain enzymes). So consequently, even if she is post menopausal, and has not had periods for a number of years, she may still have been producing oestrogen (which seems likely if she has already had a womb scrape).
As I say, please get it checked out, and hope this helps.

Hello Lemongrove,

Many thanks for your post. As you realised I’m not too clear about how the different treatments work! I understand what you are saying about hyperplasia. Juliet was diagnosed with this last year -and had a D & C in January to check that there was no sign of endometrial cancer. All seemed ok at that time - although she was told to report back if she had any bleeding (the initial symptoms had been increased discharge rather than bleeding). She has now had a bleed - and we are getting this checked out. However, I guess what I wondered was whether the change from Tamoxifen to Letrozole may have triggered a period. She was pre-menopausal at diagnosis (aged 39) but her periods stopped during chemo and did not reappear while she was on Tamoxifen. 2 months after changing to Letrozole her hot flushes stopped and she has had what appears -in length, heaviness and side effects, to be a period. At one point in our discussions with the oncs as to whether she was post menopausal I thought they said that if she turned out not to be post menopausal after all she might restart her periods with Letrozole, and if this happened she should stop taking it immediately as it could be detrimental.

I’m not sure if any of this makes sense -but was wondering if anyone else had been told this or had this experience.

With best wishes,


Hi Sharon
I’ve been on letrazole for a year now after chemo for secondaries. I wasn’t menopausal before chemo but haven’t had a period since starting chemo. My onc gives me blood tests to make sure I am not post menopausal as he says the letrazole doesn’t work if I’m having periods. On a positive side, letrazole is a very very good drug and has worked miracles on my liver mets so I hope it works for your partner.

Hi Sharon,
Again, I’m not a medic, so please, you must get things checked out properly, and take qualified advice
However, the comment i would make is that I doubt Letrozole has caused your partners bleed (at least, not in the way you suggest). Because from what you have said, your partner is most likely post-menopausal. I say this because, you mention that she has been diagnosed with endometrial hyperplasia, and has already had a scrape. Consequently she must be post menopausal (because if she were pre-menopausal she probably wouldn’t have the problem of unopposed oestrogen - which causes endometrial hyperplasia). Consequently, Letrozole is appropriate for her.
I would hazard a guess that the reason she had a break through bleed after starting Letrozole is that Letrozole has stopped her producing Oestrogen (so her body is no longer being stimulated to thicken the endometrial lining). If my guess is correct, then it’s probably a good thing, because had she remained on Tamoxifen, she would have continued to produce unopposed Oestrogen, and the endometrial lining would have continued to thicken (and eventually that could have led to serious problems).
But as I said at the beginning, please take medical advice ( I would also request an ultrasound examination of her womb,just to check the endometrial problem has resolved).

Hi Sharon,
I haven’t been on Letrozole, but I thought I might share this with you as it could be the same thing with your partner. I was diagnosed in 2005 age 41, I had a baby in the Sept 2004 and when I was diagnosed my cycle was back to normal. I had chemo first and had my last period April 2004, after chemo and mast I was put on Tamoxifen I was on that for 18 months and I spoke to the Onc and said that the side effects were awful can could I have something else. They agreed to do blood test to see if I was now post menopausal as I hadn’t had a period for over 2 years. The blood tests came back that I was and they changed me to arimadex, everything was fine apart from hot flushes. Around July this year I started to feel really well the hot flushes had all but stopped and I was sleeping well (no hot flushes waking me up every 2 hours!) and everyone said how well I was looking. Around this time I also started to get an egg white consistency odourless discharge (which I used to get when I was ovulating pre diagnosis) I then had a bleed in August. I was seen at the hospital and had scans, internal and smear and everything came back as fine and the doctor said that he thought I had had a period, when I queried this and said but I am post menopausal at least 4 years without a period he said that because I had a chemical menopause that it is not quite the same as a natural menopause, and although you don’t see this in text books he has seen periods come back after all this time in women who had gone through the menopause. This month I have had the same symptoms and had another bleed, just for 1 day, but as you say accompanied by the usual mood swings etc., The Doctor has said that as long as the bleeds are accompanied by the discharge, mood swings etc then don’t worry, but if anything changes then come straight back.
As I say not the same exactly but could be another reason to pursue. I am feeling a bit strange about it all and a bit narked that I have had all these hot flushes (bad nearly every hour) for 5 years and thought that I was getting over that, now with the prospect that I may have to go through the menopause all over again!
Hope this helps.

Tess x

Dear all,

Thanks so much to you all. I don’t use the forums much now but everytime I do I’m amazed by the supportiveness and brilliant advice from everyone. One thing that your responses -and our own experience - makes clear is that the whole pre /post menopausal thing is a grey area when complicated by bc treatments.

Louise -I’m so glad Letrozole is working for you, and I really want my partner to be able to carry on taking it too. I believe that you’ve an op coming up next week -all the very best of luck for that.

Tess- This does confirm what we suspected could happen. Your comments about it being a bummer to face going through the menopause a second time do ring very true to us as well!

Lemongrove - I am so impressed with your knowledge and you’ve given us a lot to think about. You’ve also given me some hope that Juliet can continue to take Letrozole. We’re going to chase up the GP and hospital next week and now feel much better armed to ask questions.

with love to you all - I’ll let you know what happens.


Dear all,

An update…and more questions! After Juliet’s October ‘bleed’ she went to her GP who sent a letter to the Oncs. Heard back from them to stop taking tablets (which she had already done) until they decided what to do. Recently given an appointment for Christmas Eve (!) A couple of days ago she started another bleed. Again accompanied by usual pre-menstrual symptoms, but bleed heavier and more panful than in past. So…I would like to ask if anyone has had the breakthrough bleed that Lemongrove descibes more than once, or whether this does look like the dreaded periods have returned.

The appointment letter from the onc did seem to suggest that they thought it would be periods returning and that we could discuss options in next appointment. Options seem to be just giving up letrozole, but going back on it if no bleed for a year, or chemical suppression of ovaries. By this I assume they mean zolodex. I’m not sure if oophrectomy is an option but I’m hoping we can discuss this as well. I’d be very interested in anyones experience of having to make this sort of choice and how they have found the treatment. I think that Juliet is very wary about any more interventions, and would be tempted just to give up treatment. I totally understand how she feeels, though would in my heart like her to try everything and give herself the best chance of long term survival. I think the more information, and peoples experiences, we have will help her make up her mind.

Best wishes to you all,


Or letrozole, zolodex and periods now!

Dear all,

Several months on and another update and question. Juliet eventually had a blood test which showed she was peri-menopausal. Chose to go with zolodex injections in order to start the letrozole again. There have been some real delays getting all this sorted but she had the Zzlodex inplant last week…and by the next day had started a bleed! The side effects pamphlet does mention this as a possible side effect but she is a bit wary about starting the letrozole next week as planned. Don’t have onc appointment until Xmas so would be helpful to know if any one else has experienced this.

With all best wishes,



I was on Tamoxifen for 3 years and switched to Letrozole this January after two years of having regular blood tests to show I was post-menopausal (no periods for 4 years). On Sept 13th I started bleeding after a couple of days of the dragging stomach pains and headaches. My GP has sent an urgent referral to a gynaecologist to investigate and also said the blood tests are not accurate as hormone levels can fluctuate widely!

I am interested to know what they said was the cause for your partner. Was it periods starting again? In my case I just found it strange that just as ‘Femara’ came off licence and I was prescribed a generic version of Letrozole my flushes and night sweats stopped, aching joints disappeared, having not slept for four years I suddenly started sleeping through the night, and this bleeding started. Coincidence or something more sinister with the medication?

I’m sorry I don’t have any answers for you but keep me updated and I’ll do the same when (if)I get some answers.


Hello Jo,

When Juliet first had a bleed she also had a gynaecologist referral. She had been on Tamoxifen for best part of 5 years and had some thickening of the womb lining. Gynae did D & C which showed everything ok. I think Onc then decided it was probably periods coming back -though she did think it might be a last ‘clear out’ (!) and would not happen again. Onc thought best to come off letrozole for a year to see if any more bleeding. Meanwhile J did have a couple more ‘periods’ but we also asked Onc if she could have a blood test to check her menopausal status. This was really because she wanted to carry on treatment asap rather than wait for a year - and was prepared to go for zolodex / ooophrectomy. As it was it took ages to get bloods done, and by time they were (and shoed her to be perimenopausal) she was having a fairly regular bleed - so we assumed this was periods back. She had hoped that once she started zolodex the periods would stop -but got a bleed straightaway. Will let you know how things go on. I think if it happened again, especailly once she starts letrozole, we’d have to take advice from the Onc.

It is interesting what you say about letrozole and femara. Does make you realise if there is something different (or lacking) in the generic version. I would be very interested to hear anything you find out. I would suspect that your bleeding is to do with the change of tablet rather than anything more worrying -but good luck with the gynaecologist. I do remember that the Onc thought that one reason to think the bleeding was period related was the onset of the usual premenstrual feelings - which sounds like what you have too.

All best wishes,


I have my ‘urgent’ appointment (requested on 15th Sept!) with the gynaecologist tomorrow. Haven’t had any more bleeding but have a nice bloated tummy and am peeing about every hour and a half! Am hoping it is something as straightforward as fibroids and nothing worse. Can’t help but worry a bit though.

Will let you know the outcome and any information I find about Letrozole.


Hello Jo,

Hope that the appointment went ok and that you can get this sorted out. Just to say that Juliet hasn’t had another bleed with the letrozole - so keeping fingers crossed that was a one off.

All the best,

Sharon x

Just wondered if any of you still stay connected to this forum. I have been searching for a post on letrozole and bleeding I would be interested to see what results any of you had. I have been on letrozole for about 18 months and was advised to stop taking for a few weeks to see if my joint pain got a little better. When I started taking it again I have started to bleed it’s just like a period I’m wondering if this has happened because of the six week gap. Ithe would be good to hear from anyone about my problem x