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Tamoxifen and tumor shrinkage


Re: Tamoxifen and tumor shrinkage

Hi Pye


Thanks for posting.


Many people have been in contact wondering how treatment changes due to the coronavirus (COVID-19) may impact them.  Changes are being made to treatments and the way services are delivered to minimise the risk of coronavirus to people. 


For some people, it may be safer to delay surgery and start on hormone treatment such as tamoxifen, as is the case for you. Tamoxifen may be used as the first treatment for breast cancer. This may be when surgery needs to be delayed. It’s sometimes given before surgery (known as neo-adjuvant or primary therapy) to shrink a large breast cancer so that breast-conserving surgery may be possible, rather than a mastectomy.


Although research papers may discuss response rates, it’s not possible to predict how quickly you as an individual will respond to tamoxifen and how much your tumour is likely to shrink as this can vary from person to person. Also it would appear data regarding neoadjuvant hormone therapy for premenopausal women is limited to early trials (phase two) so not enough is known yet to provide more detailed information.


It may be more helpful to speak to your treatment team and ask how often they will be monitoring you whilst you are on tamoxifen.  Decisions about treatment are made on a case by case basis by the multi-disciplinary team (MDT)  after considering the benefits and risks of treatment and other factors such as someone’s general health.   


It is common to have imaging performed at regular intervals to see how much the tumour is shrinking, and depending on this they may be able to give you some guidance on how long they expect you to remain on the tamoxifen and if it is possible for you to avoid a mastectomy. 


Do call our Helpline if you would like to talk this through or have any further questions. Your call will be confidential, and the number is free from UK landlines and all mobile networks.


You may also be interested to know that we offer a range of free supportive services.


The number is 0808 800 6000 (Text relay prefix 18001).


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Best wishes




Breast Cancer Now Nurse


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Tamoxifen and tumor shrinkage



Due to the Covid-19 situation my surgery is delayed and I've been put on Tamoxifen. 


Now I have started down this path I'd like to take the Tamoxifen for long enough to see if I have a positive outcome regarding my tumor shrinking and perhaps being able to avoid a mastectomy.  However I'm struggling to find much in the way of actual data and studies. Just seeing fuzzy answers such as 'some women' and 'may shrink'. I spoke to my breast care nurse and she was very positive from the experiences she had seen, but unable to provide any data. 


Are there any that you can point me to? The type of questions I'd like to see addressed in studies are:


  • how long Tamoxifen is taken for before results are seen
  • how long it is taken for in order to gain maximum shrinkage of the tumor
  • the % of women who do see shrinkage
  • the % by which tumors shrink

For info I'm 50, pre-menopausal and my lump is 55mm. 


Hope you can help,

With thanks,