Breast cancer is the most common malignancy in women, and its incidence is increasing year by year. While systemic combination therapy (e.g., Chemotherapy, endocrine therapy, targeted therapy, etc.) can increase the cure rate of patients, it can also bring about some adverse effects that can negatively affect the life of patients. The most common form of chemotherapy, for example, is chemotherapy drugs (especially cyclophosphamide-containing chemotherapy regimens), which can lead to impaired ovarian function. Inhibition of ovarian function with gonadotropin-releasing hormone agonists (GnRHa) can achieve protection of the ovaries during chemotherapy and help restore ovarian function. As the trend towards younger breast cancer has become more pronounced in recent years, ovarian protection has also received increasing attention. However, ovarian protection can also dramatically reduce serum estrogen levels in patients, leading to vulvovaginal symptoms such as vaginal dryness, difficulty with intercourse, genital skin irritation, itching, burning, and increased vaginal discharge. Moreover, patients are often too shy to express these symptoms, leading to underdiagnosis and under-treatment.

The North American Menopause Society states that topical estrogen therapy is the first-line option for moderate to severe vulvovaginal symptoms, but its safety in women with breast cancer is not known. Some studies have shown an increase in serum estradiol levels with the use of estradiol vaginal rings and creams, and there are no clinical studies to suggest a relationship between a mild increase and the risk of breast cancer recurrence. and short-term effects are limited. --The hierarchy is not out: hormonal therapy first, then non-hormonal therapy The onset of vulvovaginal symptoms is primarily due to a decrease in serum circulating estrogen in women, but many researchers are beginning to explore whether these changes can be attributed to changes in the dynamics of the vaginal microbiome. The vaginal microecology of healthy women is dominated by lactic acid bacteria, which proliferate in the anaerobic environment of the vagina, producing various antimicrobial compounds such as lactic acid, hydrogen peroxide (H2O2) and bacteriocins and maintaining vaginal health by enhancing epithelial barrier function, symbiotic colonization, blocking pathogenic bacterial adhesion, lowering pH, influencing antimicrobial peptide production/secretion and overall mucosal immunity. In patients presenting with vulvovaginal symptoms, vaginal microecology is no longer dominated by lactobacilli and it has been shown that the severity of vaginal dryness, dyspareunia, and vaginal pain symptoms are negatively correlated with the number of lactobacilli in the vagina. To address this issue, researchers have explored the fact that Donders et al. found that Lactobacillus combined with low-dose estrogen significantly improved vulvovaginal symptoms in women but caused a concomitant increase in serum estradiol, the risk of which is not yet known in breast cancer patients , whereas this study explored the use of Lactobacillus alone as an intervention to see if there was an increase in serum estradiol after the intervention, and prophylactic medication was administered to address patients who endure vulvovaginal symptoms due to shyness of expression. However, there is a lack of large randomized controlled clinical studies to determine the effectiveness of Lactobacillus in modulating or restoring a dysregulated vaginal microbiome and improving vaginal symptoms in different populations. The aim of this study was to explore, in the small sample size, whether prophylactic use of Lactobacillus vaginalis capsules during ovarian protection in breast cancer patients could prevent vulvovaginal symptoms in patients and to assess its safety in order to improve treatment adherence in breast cancer patients and improve the quality of life of breast cancer patients.