Question explored with the scientific record
Conversation so far
- 1 bioidentical hormones pros and cons
- 2 Is there strong evidence that bioidentical hormones work better than standard HT?
- 3 Is there any safety data for estradiol
- 4 What endometrial cancer or bleeding risks come with bioidentical progesterone?
- 5 What are the known endometrial cancer rates with estradiol+progesterone?
Answered on this page ↓
What are the known endometrial cancer rates with estradiol+progesterone?
The short version: the published cancer rates for estradiol plus progesterone are very low in short trials, but no long-term study in this retrieval tracked actual endometrial cancer incidence.
The REPLENISH trial for the combined estradiol-progesterone capsule (Bijuva) provides the best data here. At 12 months, the upper bound of the 95% confidence interval for endometrial hyperplasia was 1.06% for the 1 mg dose and 0.98% for the 0.5 mg dose [3]. That is a surrogate endpoint, not cancer itself. The study found 2 breast cancers in the higher-dose arm, 1 in the lower-dose arm, and 0 in placebo, but these numbers are too small to draw conclusions [3].
An older continuous-combined study using 17β-estradiol and dydrogesterone reports a more granular picture across 960 women [2]:
| Dose group | Total women | Proliferative endometrium | Hyperplasia | Success rate (atrophic/inactive) |
|---|---|---|---|---|
| Low dose (1 mg E2 + dydrogesterone) | 650 | 4 | not separately reported | 93–98% across dose levels |
| High dose (2 mg E2 + dydrogesterone) | 310 | 5 | 2 | 85–98% across dose levels |
The 1982 study using continuous estradiol pellets in 1,058 women found only 5 endometrial cancers over 1–21 years [1]. But that is estrogen-only therapy plus inserted pellets over a long period in a non-randomized design, so it does not directly answer the question about combined therapy.
What matters most is what is missing. No study here followed women for more than 5 years to count actual endometrial cancer cases. The REPLENISH trial stopped at 12 months of biopsy data [3]. The dydrogesterone study was a one-time biopsy snapshot [2]. Endometrial cancer takes years to develop from hyperplasia. A 12-month biopsy showing no hyperplasia is not the same as a 10-year cancer incidence study. The manufacturer funded the REPLENISH trial, and the long-term outcome the patient actually cares about, invasive endometrial cancer, was never measured.
My call: the short-term hyperplasia rates from combined estradiol-progesterone are low, likely below 2 in 100 women in the first year, but no long-term cancer incidence data exists in this retrieval. That is absence of evidence, not evidence of safety. Confidence: low.
Sources used 3
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The protective role of progesterone in the prevention of endometrial cancer
This study investigates the protective role of progestogens against endometrial cancer in women receiving estrogen therapy, highlighting that progestogens can reduce the incidence of cancer and hyperplasia, although complete protection is not yet achieved.
DOI: 10.1016/s0344-0338(82)80072-1 -
Endometrial safety of continuous combined hormone replacement therapy with 17β-oestradiol (1 or 2 mg) and dydrogesterone
This study investigates the endometrial safety of continuous combined hormone replacement therapy using 17i-oestradiol and dydrogesterone, demonstrating that doses of dydrogesterone at 5 mg or higher effectively prevent endometrial proliferation in postmenopausal women.
DOI: 10.1016/s0378-5122(00)00176-6 -
Estradiol and Progesterone (Bijuva)
Fixed-dose estradiol-progesterone (Bijuva) significantly reduces frequency and severity of vasomotor symptoms and improves menopause-related quality of life in postmenopausal women with an intact uterus, with endometrial safety observed over 12 months, though long-term harms and…
DOI: 10.51731/cjht.2022.306