Progesterone Positive??

Hi All

Does anybody know why it is “good” if your tumour is progesterone positive as well as oestrogen positive. I know tamoxifen blocks the oestrogen but what is blocking the progesterone?? My onc said it is better to be progesterone positive too but I don’t know why?

Does anyone have a clue?

Love Alise

Hi Alise,

I am glad you raised this question as I have been wondering the same thing myself.I am oestrogen and progesterone positive, and while there is loads of info on the oestrogen side of things, I can find nearly nothing on being progesterone positive.
Also what does progesterone do in the body? And did being on the mini-pill (progesterone only) accelerate my breast cancer.? All questions I would love to ask my onc, but A. there never seems to be enough time to ask him, and B. I feel a bit stupid asking as I think he will think it a petty, and to be honest, not a relevent question any more.


As I understand it!

Progesterone is naturally secreted by the ovary in the second two weeks of the menstrual cycle in reproductive age ovulating women. Progesterone or progesterone-like substances are also ingested in birth control pills, hormone replacement therapy, or just sometimes to induce a period or regulate abnormal bleeding problems. Progesterone has been used also as therapy for PMS syndrome and for women with infertility or frequent pregnancy loss.

Many invasive breast tumours are oestrogen or progesterone receptor positive. This means that the cancer cells express receptors for these hormones on their surface. Adjuvant endocrine therapy describes the treatment of these cancers with additional hormone drugs. Adjuvant endocrine therapy is usually given after surgery and radiotherapy but women may also be treated with adjuvant endocrine therapy prior to, or subsequent to, chemotherapy.

Adjuvant endocrine therapy is recommended for women with tumours that have been assessed as responsive to hormone treatment, also known as hormone-responsive BC. To determine if the BC will respond to hormones, an oestrogen/progesterone receptor test is carried out on the tumour. If positive, the patient will normally be prescribed adjuvant endocrine therapy.

Hormones are secretory substances that control the growth and activity of normal cells. In BC, both the female hormones, oestrogen and progesterone, have been shown to have a growth-promoting impact on certain BC cells. Depending on the particular type of hormone treatment used, adjuvant endocrine therapy exerts its effects either through the blockage of oestrogen production or by preventing oestrogen from reaching its target receptors on cancer cells.

Tamoxifen is perhaps the most commonly used adjuvant endocrine therapy. It is an anti-oestrogen drug which works by preventing the hormone from attaching to breast cancer cells and encouraging them to grow.

Aromatase inhibitors – anastrozole (Arimidex), exemestane (Aromasin), letrozole (Femara) - block the small amount of oestrogen that is produced by the adrenal glands which lie just above the kidneys. They work by inhibiting the activity of the enzyme, aromatase, which is needed to convert androgen hormones into oestrogen. These drugs are used in post-menopausal women whose ovaries have shut down and where the only remaining source of oestrogen production is via the adrenal route. AIs are used to treat post-menopausal women with early BC in order to reduce risk of recurrence. They may be used as an alternative to, or subsequent therapy to, Tamoxifen.


Thank you margaret - very impressive.!!!

However - does the tamoxifen stop the progesterone attaching to cancer cells as well??

Love Alise

Hi Alise,

I believe that Tamoxifen works on the whole body by blocking the effects of oestrogen and progesterone on cancer cells. Am sure someone will know more!

Margaret x

I think that tamoxifen is supposed to work better with PR+ bc; better, that is, than with ER+ PR- cancers.
The concentration of ER can affect response to tamoxifen too. They use something called the Quick score in which ER is given as a score out of 8 where 8/8 = strongly ER +
In the days before adjuvant therapy was routinely offered to node negative patients, there was indication that a lot of progesterone receptors tended to suggest a better prognosis. I don’t know why! Now that they’ve found out that some cancers are resistant to tamoxifen (the PR- ones which can resond better to AIs) the PR seems to be an important marker again.


I have reopened this thread as I still do not fully understand.

I am ER+ and PR+. I have only just discovered that I am PR+ after sorting out some papers. I had always thought I was just ER+. Not sure if being PR+ as well as ER+ is good news or not - if anything is good news about bc!

I have been on Arimidex since diagnosis 2 1/2 years ago and now I am not sure if this is the best medication to be on. I was on Tamoxifen for 2 months but I instigated the change to Arimidex. Now I am not sure if I did the right thing.

Can anyone explain in simple words as my brain is Arimidex fuzzy!

Christiane x

Hi Christiane

You may find that the Breast Cancer Care Helpline can answer your questions and explain things to you. You can call the helpline on 0808 800 6000
Monday to Friday 9am-5pm and Saturday 9am-2pm. The staff on the helpline can also talk through the complexities of different treatments and conditions.

If you would prefer you can use the BCC ‘Ask the Nurse Service’ for which I have posted the link below, they will be able to offer further support and advice but due to the number of emails they are receiving at the moment it may take time to receive a reply.

I hope this helps.

Kind regards

BCC Facilitator

Without wanting to offend anyone who isn’t PR+ I understand there is a considerably higher success rate with hormone therapy for those women who are PR+ as well as ER+. This I have learnt from a cancer website but can’t remember which one.


I am only pr+ and was told by my oncologist to take tamoxifen but they are not sure of the overall effectiveness of this drug in my situation. anyway just had ovaries removed on oncologists advice, its all so confusing!!!

Hi Christiane and Annamarie,

Glad this thread has popped up again because I keep wondering about PR. I am like you Anna ER- but PR+ (89%) and I am currently on tamoxifen. I can’t find much information on the internet about ER-/PR+ except that it only occurs in about 5% of breast cancer patients. At my consultation I was only given statistical benefits for surgery, rads, chemo and herceptin so have no idea how much tamoxifen will benefit me. If I find anything worthwhile on PR+ only I will post back but don’t hold out much hope. Love xxx

I also wonder about this. I am ER-/PR+ plus HER2. I was told tamoxifen/Arimidex would have partial benefit to me. I was told I scored 8 for progesterone and then only when I pressed for info. I guess the more things you are positive for the more treatment they can offer anyway.

Hi Starfish,

You are the first person I have come across with a similar dx i.e. ER-/PR+ and HER-2+. I don’t feel so much on my own now!! I only found out I was PR+ because I was nosey and looked through my chemo notes which the nurse had left on the table! Like you, am quite happy to take anything they can give me as I have two young children but I would still like to know a bit more about PR+. Love xxxxx

I am ER- and PR+ when i was put on tamoxifen 2 years ago i asked if it worked on people who were only PR+ as all you every read about is ER+, she said that it works for PR as well.
Now i have been put on Femera, have already started to loose weight and feel as though i have more energy. I asked my onc about Femara and he says that they are getting good results from it with pre menopausale too !!! Just want to add that i am in France.

I suspect I may go onto Femara as well after Arimidex. They are currently testing my hormone status which I request last time. I have just started chemo. I have read somewhere on here that Arimidex is better for progesterone plus but I may be wrong. Initially onc said he would put me on Tamoxifen for 2 years, Arimidex for 2 years and something else after that. I am also HER2 so will have injections for that as well. Just hope it all works!!