Results
Two-sample MR Analysis of sex Hormones and Breast Cancer Risk
To investigate the effect of sex hormones on BC risk, we conducted an MR analysis of nine hormones and SHBG on overall, ER+ and ER–BC risk.
After clumping at R 2 < 0.001, we identified 204 and 131 SNPs to proxy for an SD increase in TT and BT at P ≤ 5 × 10–8, respectively (Additional file 1: Table S1). These SNPs explain 2.36% and 1.77% of the variance in the hormone levels and have an F statistic of 27.29 and 25.87, respectively (Additional file 1: Table S2). Using an IVW approach, we found that an SD increase in TT increased the risk of overall BC and ER + BC (OR 1.14, 95% CI 1.09–1.21 and OR 1.19, 95% CI 1.12–1.27, respectively) but had no effect on ER–BC (OR 0.99, 95% CI 0.93–1.06) (Figure 2). We also found positive associations between TT and overall BC risk using the MR-Egger, weighted median and weighted mode methods (OR 1.22, 95% CI 1.10–1.34, OR 1.13, 95% CI 1.06–1.20 and OR 1.17, 95% CI 1.08–1.26, respectively) as well as a positive association with ER + BC risk (MR-Egger OR 1.29, 95% CI 1.16–1.45, weighted median OR 1.17, 95% CI 1.09–1.27 and weighted mode OR 1.23, 95% CI 1.13–1.35) (Additional file 1: Table S3). Furthermore, we conducted an MR-Egger intercept test but found no evidence of directional pleiotropy for overall BC risk and ER + BC risk (Additional file 1: Table S4).
Figure 2.
Forest plot showing the MR associations between sex hormones and overall, ER+ and ER–BC risk. IVW analysis was carried out to assess the association between an SD increase in total testosterone, bioavailable testosterone, SHBG, DHEAS, estradiol, androstenedione, aldosterone, cortisol, progesterone and 17-OHP on risk of incidence of overall BC (black), ER + BC (grey) and ER–BC (red). OR odds ratio, TT total testosterone, BT bioavailable testosterone, SHBG sex hormone-binding globulin, DHEAS dehydroepiandrosterone sulphate, E2 estradiol, ANDRO androstenedione, ALDO aldosterone, CORT cortisol, PROG progesterone, 17OHP 17-hydroxyprogesterone
We also found that an SD increase in BT increased the risk of overall and ER + BC (OR 1.19, 95% CI 1.07–1.33 and OR 1.25, 95% CI 1.11–1.40, respectively). Further positive associations were found using the weighted median approach (overall BC risk: 1.13, 95% CI 1.02–1.24 and ER + BC OR 1.23, 95% CI 1.10–1.38) and suggestive positive associations from the MR-Egger and weighted mode approaches (Additional file 1: Table S3).
We found two SNPs at P ≤ 5 × 10–7 to proxy for an SD increase in estradiol, which explained 0.64% of the variance with an F statistic of 8.40. Although the F statistic is low, one of the SNPs (rs2414098) is an intronic variant in the gene CYP19A1[56] which encodes the enzyme involved in the conversion of testosterone to estradiol.[37] For this reason, we continued with the MR analysis and found an increased risk of both overall BC risk and ER + BC (OR 1.03, 95% CI 1.01–1.06 and OR 1.06, 95% CI 1.03–1.09, respectively) but no effect on ER–BC risk (OR 1.01, 95% CI 0.96–1.05).
Due to the possibility of weak instrument bias, we also used the MR-RAPS method and found a positive association between an SD increase in estradiol with overall and ER + BC (OR 1.04, 95% CI 1.01–1.06 and OR 1.06, 95% CI 1.02–1.09, respectively). Since only two SNPs were used as proxies for estradiol, no other MR methods were used to test this association. We also calculated the genetic correlation between TT and BT with estradiol, but found no strong evidence of correlation (TT rg: 0.25 (95% CI − 0.05–0.54) and BT rg: 0.09, (95% CI − 0.13–0.31)) (Additional file 1: Table S5), indicating that the effect of estradiol on BC risk may be independent of testosterone levels.
Similar to TT, BT and estradiol, we found a positive association between an SD increase in DHEAS (proxied by 4 SNPs) and ER + BC risk (OR 1.09, 95% CI 1.03–1.16), with positive associations also observed using the weighted median, weighted mode and MR-Egger approaches (OR 1.08, 95% CI 1.04–1.13, OR 1.08, 95% CI 1.03–1.13, OR 1.07, 95% CI 0.97–1.18, respectively) (Additional file 1: Table S3).
We found little evidence of association between SHBG or cortisol levels and overall, ER+ and ER–BC risk. With regards to androstenedione, aldosterone, progesterone and 17-OHP, we also found little evidence of associations with overall, ER+ and ER–BC risk. However, we acknowledge that the genetic instruments used to proxy these hormones may be weak as demonstrated by low F statistics (0.78–3.79)[57] (Table 1). For this reason, we also carried out a weak instrument robust method—MR-RAPS, but still found little evidence of an association between the four hormones and overall, ER+ and ER–BC risk (Additional file 1: Table S3).
Two-sample MR Analysis of sex Hormones and Breast Cancer Subtype Risk
To investigate the effect of sex hormones on the risk of specific BC subtypes, we conducted an MR analysis of the nine hormones and SHBG on luminal A-like BC, luminal B-like BC, luminal B/HER2-negative-like BC, HER2-enriched-like BC, TNBC and BRCA1-mutated TNBC. Details on the SNPs used as instruments in this analysis are found in Additional file 1: Tables S6 and S7.
We found that an SD increase in TT levels increased the risk of luminal A-like BC, luminal B-like BC and luminal B/HER2-negative-like BC (OR 1.21, 95% CI 1.13–1.28, OR 1.14, 95% CI 1.02–1.26 and OR 1.21, 95% CI 1.11–1.31, respectively) (Figure 3). Similar directions of association were found using the weighted median, weighted mode and MR-Egger approaches (Additional file 1: Table S3) with the MR-Egger intercept showing no evidence of directional pleiotropy (Additional file 1: Table S4). Conversely, an SD increase in TT was associated with a decreased risk of BRCA1-mutated TNBC (OR 0.91, 95% CI 0.84–0.99). We found positive associations between an SD increase in BT and luminal A-like BC and luminal B/HER2-negative-like BC risks (OR 1.29, 95% CI 1.15–1.43 and OR 1.22, 95% CI 1.07–1.40) with consistent directions of association found using the weighted median, weighted mode and MR-Egger approaches for the association with luminal A-like BC. However, only the MR-Egger approach showed a positive association for luminal B/HER2-negative-like BC risk (Additional file 1: Table S3). In contrast, the MR-Egger intercept showed little evidence of directional pleiotropy for any of these associations (Additional file 1: Table S4).
Figure 3.
Forest plot showing the MR associations between sex hormones and risk of six BC subtypes. IVW analysis was carried out to assess the association between an SD increase in total testosterone, bioavailable testosterone, SHBG, DHEAS, estradiol, androstenedione, aldosterone, cortisol, progesterone and 17-OHP on risk of luminal A BC (black), luminal B (grey), luminal B and HER2-negative BC (red), HER2-enriched BC (green), triple-negative BC (blue) and BRCA1 mutated triple-negative BC (purple). OR odds ratio, TT total testosterone, BT bioavailable testosterone, SHBG sex hormone-binding globulin, SHBG adjusted SHBG adjusted for BMI, DHEAS dehydroepiandrosterone sulphate, E2 estradiol, ANDRO androstenedione, ALDO aldosterone, CORT cortisol, PROG progesterone, 17OHP 17-hydroxyprogesterone, TNBC triple-negative BC
We found an inverse association between an SD increase in levels of SHBG and luminal A-like BC risk (OR 0.84, 95% CI 0.73–0.97); however, the weighted median, weighted mode and MR-Egger approaches showed little evidence of association (Additional file 1: Table S3).
Similar to TT and BT, we found that an SD increase in estradiol increased the risk of luminal B/HER2-negative-like BC (OR 1.08, 95% CI 1.02–1.14) and a possible inverse association with the more aggressive subtype of cancer (TNBC IVW OR 0.95, 95% CI 0.88–1.01) (Figure 3). We also found similar associations using the MR-RAPS method (OR 1.08, 95% CI 1.01–1.15 and OR 0.94, 95% CI 0.89–1.00). Due to a limited number of SNPs, further MR methods could not be applied.
We also found positive associations between an SD increase in DHEAS and luminal A-like BC, luminal B-like BC and luminal B/HER2-negative-like BC (OR 1.06, 95% CI 1.02–1.11, OR 1.11, 95% CI 1.00–1.22 and OR 1.09, 95% CI 1.01–1.19, respectively) and found concurring results with the weighted median approach for all subtypes and suggestive positive associations for both the weighted mode and MR-Egger approaches (Additional file 1: Table S3). We saw little evidence of directional pleiotropy from the MR-Egger intercept (Additional file 1: Table S4).
With regards to cortisol, we found an inverse association between an SD increase in the hormone and HER2-enriched-like BC (OR 0.45, 95% CI 0.22–0.92). The F statistics and variance explained for the remaining four hormones (androstenedione, aldosterone, progesterone and 17-OHP) were suggestive of weak instruments and power calculations showed that we were underpowered to detect an effect for some of the BC subtypes (Additional file 1: Table S8). We found a positive association between androstenedione and luminal B-like BC using the IVW method (OR 1.08, 95% CI 1.01–1.15), but this effect was no longer observed using the weak instrument—robust MR-RAPS method (OR 1.02, 95% CI 0.99–1.05). The MR-RAPS method did suggest a possible association of androstenedione with TNBC (OR 1.08, 95% CI 1.00–1.17). We found little evidence of associations between aldosterone and progesterone with the risk of the six BC subtypes using both the IVW and MR-RAPS method. Finally, we observed a positive association between an SD increase in 17-OHP and luminal A-like BC (OR 1.01, 95% CI 1.00–1.03) and an inverse association with BRCA1-mutated TNBC (OR 0.97, 95% CI 0.95–0.98) using the IVW method. Both of these associations were also observed when using the MR-RAPS method (luminal A-like BC OR 1.01, 95% CI 1.00–1.03 and BRCA1-mutated TNBC OR 0.97, 95% CI 0.95–0.99).
Breast Cancer Res. 2022;24(66) © 2022 BioMed Central, Ltd.
Copyright to this article is held by the author(s), licensee BioMed Central Ltd. This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original citation.
