A window of opportunity study to assess the biological effects of progesterone in premenopausal ER-positive, PR-positive early breast cancer


Treatment with progesterone has shown consistent benefit in women with advanced ER+ breast cancer who have relapsed on prior endocrine therapy. More recently, activation of the progesterone receptor has been shown to reprogramme the oestrogen receptor and reduce proliferation of breast cancer cells.

PEARL aims to assess the effect of oral micronised progesterone/Utrogestan (chemically identical to progesterone of ovarian origin) in combination with Tamoxifen as compared to tamoxifen alone on breast cancer proliferation as measured by Ki67.


PEARL aims to determine whether 2 weeks of treatment with Utrogestan (oral micronised progesterone) plus Tamoxifen in early ER+ PR+ breast cancer patients results in a reduction in tumour cell proliferation (as determined by a reduction in Ki67) from baseline (pretreatment) to post treatment (at time of surgery or research biopsy prior to commencing neoadjuvant chemotherapy).


Randomisation to oral micronized progesterone plus Tamoxifen versus Tamoxifen alone

Inclusion Criteria

  • Premenopausal women aged 16 years and above
  • Newly diagnosed breast cancer
  • ER positive, PR positive
  • HER2 Negative
  • Tumour measuring ≥10mm in longest diameter by ultrasound or mammogram examination

Further Information

For further information about this trial please contact the trial coordinator at or Prof Carlo Palmieri at