The oncologic impact of hormone replacement therapy in premenopausal breast cancer survivors: A systematic review.

SYNOPSIS: This is the first systematic review to investigate the risk of recurrence in breast cancer survivors <50 years old who have used hormone replacement therapy (HRT).

BACKGROUND: The risk of HRT in premenopausal breast cancer survivors is unclear. Due to the higher incidence of estrogen receptor negative tumours in women <50, the potential for HRT to promote breast cancer recurrence may differ from older age groups.

METHODS: We performed a search of Medline, EMBASE and CINAHL through June 2016. For the observational studies relative risk (RR) and 95% confidence interval (CI) were calculated for the recurrence rate among HRT users and nonusers. A random effects model was used to estimate the combined RR using the Mantel-Haenszel method.

RESULTS: Four papers satisfied our inclusion criteria. 3477 subjects were analyzed. On pooled meta-analysis of breast cancer recurrence in the observational studies, no significant association was found between HRT and risk of recurrence (RR 1.04 [95% CI 0.45, 2.41]). The randomized controlled trial (RCT) included found an increased risk of recurrence with HRT among women <50 (HR 1.56 [95% CI 1.1-2.2]). However, among women of all ages with an estrogen receptor negative tumour there was no significant difference in recurrence when compared to hormone receptor positive tumours (HR 1.15 [95% CI 0.7-1.8, p = 0.55]).

DISCUSSION: This review on HRT in breast cancer survivors <50 revealed conflicting results between randomized and observational study data. Further studies are warranted to investigate the association between HRT and recurrence rates in younger breast cancer survivors.