Anti-Müllerian Hormone Concentrations in Premenopausal Women and Breast Cancer Risk

Discussion

In our sample of women diagnosed with breast cancer at ages 35 to 60, prediagnosis serum AMH levels were positively associated with breast cancer risk compared with age-matched controls. The positive trend appeared strongest for women diagnosed at older ages with ER-positive tumors, although interaction tests with age and ER status were not statistically significant.

Previous experimental studies have suggested that AMH may play an important role in breast cancer risk. AMH receptors (MIS type II) are expressed in both normal and cancerous breast tissue. Contrary to our findings, several in vitro and in vivo studies have shown AMH can inhibit tumor cell growth and migration through NFkB-mediated pathways (8, 9, 19). However, these studies have focused on basal-like breast cancer models such as the C3Tag mouse model or the MCF10A cell line, and therefore may not be comparable with a study examining all breast cancers. Basal-like breast cancers represent only 15% to 20% of breast cancers overall (10, 11, 20), and distinct effects in those tumors would not be readily detectable in our sample, which included a majority of ER-positive breast cancers

Although basal-like breast cancer represents the minority of tumors overall, basal-like subtypes are proportionally more common among younger women (e.g., 26.5% of tumors at ages 40–49 vs. 17.5% at ages 60–69 in Sweeney and colleagues; ref. 21). Epidemiologic studies of AMH and breast cancer diagnosed at reproductive ages are lacking. A cross-sectional study of 30 women ages 38 to 50 undergoing breast biopsies found lower AMH levels (P = 0.0009) among women with a cancer finding versus a benign diagnosis (14). A case–control study (N = 108 cases, 99 controls) using post-diagnosis, pretreatment serum samples reported no overall association between mean AMH and breast cancer, but an inverse association among women diagnosed after age 37 (β = −0.85, 95% CI, −1.48 to −0.22). These findings are consistent with the laboratory data, but the small sample sizes and use of AMH measures collected concurrently or after breast cancer diagnosis are problematic for evaluating AMH as a predictive factor. Other elements of the case–control study design also limit interpretation: Cases were identified from oncology clinics in Pennsylvania and California, whereas controls were North Carolina residents participating in a fecundability study. Furthermore, the median age at enrollment was 40.2 years among cases and 33.9 among controls (15).

One prior epidemiologic study analyzed prediagnosis AMH concentrations in relation to breast cancer risk, and unlike the other reports, observed a positive association between AMH and breast cancer risk (12). Using a nested case–control design (N = 108 cases, 99 controls), AMH concentrations were measured in archived blood samples donated at an average age of 45 years. After a mean follow-up of 14 years, 105 breast cancers were diagnosed. The authors reported a 9.8-fold increase in breast cancer odds comparing fourth versus first quartile AMH (OR, 9.8; 95% CI, 3.3–28.9). This effect was most apparent among women diagnosed at ages ≥55 years (12).

On the basis of the laboratory models and few human studies, we hypothesized that the direct effect of circulating AMH on breast tissue would be antitumorigenic such that higher levels of AMH would be associated with decreased risk for premenopausal breast cancer, whereas higher relative levels of AMH before menopause would be positively associated with older-onset breast cancer as a marker of delayed menopause, an established breast cancer risk factor. In our analysis, we were unable to identify the hypothesized inverse association except by the weak, nonsignificant association among women diagnosed with breast cancer at ages 35 to 45. However, only 64 cases were characterized as ER-negative, and only a subset of these would likely meet the full definition of the basal-like subtype (10, 11).

The increased risk of breast cancer among older women with higher AMH may reflect an older age at menopause. As noted above, AMH is produced by the granulosa cells of pre- and small antral ovarian follicles. As the number of ovarian follicles is depleted over the life course, AMH levels decline until they become undetectable before menopause. In the Penn Ovarian Aging Study, women ages 35 to 48 with undetectable AMH concentrations (lower LOD = 0.10 ng/mL) had a median time to menopause of 6 years (3). Similarly, the longitudinal Michigan Bone Health and Metabolism study demonstrated undetectable (<0.17 ng/mL) AMH concentrations approximately 5 years before the final menstrual period (3). In these studies and others (22, 23), higher relative AMH concentration was a marker for delayed menopause (2, 24) within a given age group. Older menopausal age confers a small, but consistently observed, increase in breast cancer odds. In Norwegian registry data, a 1-year difference in menopausal age was estimated to confer a 4% increase in breast cancer odds (25).

Overall, our findings agree with the prior report by Dorgan and colleagues, although the magnitude of the positive association is smaller in our study. In the Dorgan study, control participants were matched 2:1 to the cases on age and other factors and were selected from a pool of premenopausal women based on menstrual status and serum follicle–stimulating hormone and estradiol concentrations. In contrast, our study was not restricted to women with hormone levels consistent with premenopausal status. Instead, we relied upon self-report of one or menstrual cycles in the previous 12 months, a common definition for menopausal status in large epidemiologic studies (26). Furthermore, for women who reported a prior hysterectomy without removal of both ovaries, we applied an age-based cutoff of <55 years to identify potentially premenopausal women. These criteria may lead to some misclassification of menopausal status and the possible inclusion of peri- or post-menopausal women. On the basis of our definition of menopause, our analytic population likely had a lower distribution of AMH levels compared with the study population in the Dorgan and colleagues report. Consistent with Dorgan and colleagues, we observed a stronger effect estimate among women diagnosed at older ages. Furthermore, we observed the same pattern of association in sensitivity analyses that excluded women with a prior hysterectomy where the misclassification of menopausal status is likely greatest.

Newly developed, ultrasensitive AMH assays allow for high-quality AMH measurement at older reproductive ages and were used in this analysis (27, 28). Nevertheless, we observed an increasing proportion of samples with nondetectable levels with increasing age from 35 to 54–50% of women 50 and older had nondetectable values. AMH levels are relatively stable across the menstrual cycle (2), and therefore are amenable to measurement in large epidemiologic cohorts, like the Sister Study, where blood draws are not timed to the menstrual cycle. However, one study of 27 women reported greater variability in AMH across the menstrual cycle at ages 45 to 55 years compared with 18 to 35 years (29); if variability is greater at older reproductive ages, our effect estimates could be biased toward the null due to exposure misclassification.

Testosterone levels have less variability across the menstrual cycle compared with estradiol and progesterone and are positively associated with pre- and post-menopausal breast cancer (30). Testosterone concentrations are also positively correlated with AMH levels (31, 32) and were controlled for in the current analysis. We did not measure estradiol levels because the blood draw was not timed to the menstrual cycle and premenopausal estradiol has a weaker association with breast cancer risk compared with postmenopausal levels (30, 33, 34). In the Dorgan and colleagues report, additional adjustment for estradiol did not influence the association between AMH and breast cancer (12).

In our study, where 75% of breast cancers were diagnosed after age 45 and 81% were ER positive, we observed a positive association between prospectively collected serum AMH and breast cancer risk. A larger sample of women with a younger age distribution or higher proportion of basal-like tumors is needed to conclusively address possible protective effects of AMH on breast cancer. Quantifying expression of AMH receptors in breast tissue and polymorphisms in the AMH and AMH type II receptor genes may also provide a more complete picture of the underlying biology in future studies.