Most recent I have seen is this from BMJ
Yana Vinogradova, Carol Coupland, Julia Hippisley-Cox. Use of hormone replacement therapy and risk of breast cancer: nested case-control studies using the QResearch and CPRD databases. BMJ, 2020; m3873 DOI: 10.1136/bmj.m3873
“Overall, 33,703 (34%) women with a diagnosis of breast cancer and 134,391 (31%) controls had used HRT recently or in the past.
Risk increases were mostly associated with estrogen-progestogen treatments, but small increases were also associated with estrogen only treatments.
For example, for recent long-term users, compared with never use there was a 15% associated increased risk of developing breast cancer for estrogen only therapy, while there was a 79% associated increased risk for combined estrogen and progestogen therapy.
Past long term use of estrogen only therapy and past short term use of estrogen-progestogen were not associated with increased risk. The risk associated with past long term estrogen-progestogen use, however, remained increased (16%).
To put these risks into context, in recent estrogen only users, between three (in younger women) and eight (in older women) extra cases per 10,000 women years would be expected, and in estrogen-progestogen users between nine and 36 extra cases per 10,000 women years.
For past estrogen-progestogen users, the results would suggest between two and eight extra cases per 10000 women years.”