With reference to Nas and CLKD's comments here are some quotes from the Position Statement For Management of Genitourinary Syndrome of the Menopause (GSM) that you might find helpful.
"Non-hormonal approaches are usually the first-line choice for managing urogenital symptoms (or related urinary symptoms) experienced by women during or after treatment for an oestrogen-receptor-positive breast cancer.
Women can usually be given local vaginal oestrogen to improve their symptoms related to GSM. For the treatment of severe GSM symptoms, there are no specific data on the safety of local vaginal oestrogen after oestrogen-receptor-positive breast cancer. However, after regeneration and cornification of the vaginal skin, increased systemic levels of oestrogen are not seen and they remain below postmenopausal levels. Such local oestrogen-only therapy, even long term – if associated with improved quality of life and sexual function – will seem a reasonable theoretical and unproven small risk to many informed breast cancer patients. Women with a history of any type of cancer – including oestrogen-receptor-positive cancer – should use vaginal oestrogen if required and if beneficial; they should continue using this in the long term. The evidence does not show an increased risk of cancer recurrence among women using vaginal oestrogen who are undergoing treatment for, or have a history of, an oestrogen-receptor-positive cancer."
The link to the full pdf document
https://bssm.org.uk/wp-content/uploads/2023/02/GSM-BSSM.pdf