Drugs used to treat prostate cancer in men may also be useful for difficult to treat breast cancers in some women, say researchers.
Hormone treatments such as tamoxifen and aromatase inhibitors are ineffective against up to 30% of breast cancers.
Breast cancers can be driven by oestrogen
The study, in The EMBO Journal, suggests some of these tumours may respond to drugs for male cancers.
Cancer Research UK said the findings were a "great surprise".
Hormones can switch on genes which lead to cells dividing uncontrollably and developing into tumours.
In women, breast cancers can be driven by the female sex hormone oestrogen. In men, prostate cancer can be driven by male sex hormones - androgens.
Breakthroughs have been made in treatments for breast cancer by developing drugs which interfere with the oestrogen's action, halting the tumour's progress.
However, tumours which are not driven by the hormone have been harder to treat.
Prostate to breast
Researchers at the Cancer Research UK Cambridge Research Institute found that some of these oestrogen negative tumours were instead influenced by male hormones.
The same genes which were switched on by female sex hormones in oestrogen responsive tumours were activated by the male sex hormones.
It raises the prospect that drugs already developed for prostate cancer could help some women.
While androgens, such as testosterone, are typically associated with male development, they are also present in women.
The lead researcher Dr Ian Mills said: "This important discovery suggests that patients with a type of oestrogen-receptor-negative breast cancer may potentially benefit from therapies given to prostate cancer patients, which could transform treatment for this patient group in the future.
"But at the moment this laboratory research is still at an early stage."
Researchers said this could apply to up to 5% of all breast cancers.
Dr Lesley Walker, from Cancer Research UK, said: "Prostate cancer depends on the androgen receptor for growth so it's a great surprise that a type of breast cancer might also be fuelled by this protein."
Dr Caitlin Palframan, policy manager at Breakthrough Breast Cancer, said: "This fascinating research opens the door to personalised treatment for a small group of breast cancer patients.
"Women with oestrogen receptor negative disease have fewer treatment options and new ways to tackle it are urgently needed.
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