Ovarian reserve and beyond: AMH’s role in women’s reproductive health

The human gene for anti-Müllerian hormone (AMH) was isolated and sequenced 20 years ago [1], with the first immunoassays developed in 1990 [2,3].  Since then, our understanding of this hormone has significantly increased, with most clinical use today focusing on women’s reproductive health. AMH’s ability to reflect the number of small antral and pre-antral follicles present in the ovaries, and therefore the ovarian reserve, has led to AMH measurement being used in a wide array of clinical applications.

One of the first was as a tumour marker in the diagnosis and follow up of women with ovarian granulosa cell tumours (GCT) [4, 5]. More recently, with the dramatic improvements in the treatment of childhood cancers, attention is focused on AMH to assess the likelihood of gonadal damage and infertility after treatment.  It is also being used to investigate the toxicity of different therapeutic regimens, in the choice of those treatments, and the prediction (and potential preservation) of fertility in young women and children following cancer therapy.

Sensitive diagnostic marker for GCT
GCT accounts for 2-3% of all ovarian tumours, with two distinct types: the juvenile and the adult form. The more common adult form generally presents in women at around 50 years. A majority have endocrine manifestations as a direct consequence of hormone secretion by the tumour [6].

GCTs have the potential to secrete estradiol, Inhibin (A and B) and AMH. Inhibin and AMH are the more useful biomarkers since estradiol is only produced in 50-60% of GCT patients and is dependent on stimulation by testosterone from adjacent theca cells. While serum total Inhibin is secreted in almost all GCT and has been shown to successfully detect recurrence following surgery, it is also increased in some epithelial ovarian tumours and fluctuates significantly within the menstrual cycle. AMH is more specific to GCT as expression is limited to ovarian granulosa cells and it does not change substantially over the menstrual cycle.

Although GCT is extremely rare, it is noted for its late recurrence, usually within four-six years, but can be up to 10-20 years after removal of the primary tumour. AMH disappears within days of removal of the ovaries [7] and, following tumour resection, a rise in AMH precedes clinical detection, making it an extremely sensitive marker for the early detection of tumour recurrence.

Lane’s 1999 study followed 56 patients post operatively and showed that AMH was useful in evaluating the completeness of tumour removal [4]. In addition, serial AMH measurements were able to detect recurrence on average three months prior to clinical detection. A second study, which followed 31 patients for up to seven years, confirmed these observations [5]. This group used an AMH assay 20 times more sensitive than previously used and, when comparing both assays found discrepant values in six out of 31 patients. The more sensitive assay accurately reflected the clinical situation and was elevated up to 16 months earlier in patients with tumour recurrence.

However, there is still insufficient published information on which to assess the sensitivity and specificity of AMH for the diagnosis of GCT.  This is due to small patient numbers, the insensitivity of older assays and the lack of solid reference values in pre-menopausal women and children. The advent of more sensitive, fully automated assays will facilitate more robust studies.

Assessment of ovarian damage
The relationship between AMH and the number of small growing follicles (and therefore the number of primordial follicles or ovarian reserve) makes it useful for assessing the gonadal toxicity of cancer therapy and loss of ovarian reserve.  Levels fall rapidly with the onset of cancer treatment, with subsequent recovery dependant on degree of ovarian damage. AMH appears to identify which treatments may spare the ovaries, or are most toxic to them, and may give clinicians additional information to direct therapeutic choices in children and women of childbearing age with cancer.

Radiotherapy is a well-known cause of ovarian damage, even at low radiation levels. Women who have undergone pelvic or total body irradiation are likely to have low or undetectable AMH levels [9, 10]. The gonadal toxicity of alkylating agents is also well established. In a study involving young women with lymphoma, those receiving alkylating agents showed little or no recovery in AMH levels following treatment whereas those receiving alternative chemotherapy showed good recovery. 

Childhood cancer and fertility
Childhood cancer treatment has improved dramatically with survival rates of more than 90%.  However, the consequences of treatment may be permanent damage to the ovaries, affecting fertility. AMH is detectable in females of all ages rising steadily throughout childhood. Several studies have confirmed its role as a clinically useful marker to assess impairment of ovarian reserve in those receiving treatment for cancer  [11, 12, 13].

Brougham showed that AMH decreased during chemotherapy in both prepubertal and pubertal girls, becoming undetectable in 50% of patients; recovery occurred in the low to medium risk groups after completion of treatment, yet remained undetectable in the high risk group.  Inhibin B was undetectable in most patients before treatment and FSH showed no relationship with treatment. Thus AMH indicates a more useful  assessment of residual ovarian reserve, revealing partial loss or ovarian failure.

It is clear that a woman can suffer a significant loss of ovarian reserve without any lasting effects on her fertility, for example following removal of an ovary.  For survivors of childhood cancer this may mean that only a substantial loss of ovarian reserve would have a clinical impact. Indeed, recent work has shown that there is a high number of successful pregnancies in lymphoma survivors, despite low AMH levels [14].  In a study of 84 childhood cancer survivors they achieved pregnancy rates similar to controls despite impaired ovarian reserve [15]. However, a 10-year follow up study of childhood cancer survivors, now in their 30s, showed that the percentage of childless women in this group was greater than in the normal Danish population, particularly in the group of women who received the most gonadotoxic treatment burden. Their pregnancy rate and outcome was especially poor [16].  The truth is difficult to discern on current evidence and more work is required on long term follow up, with fertility and age at menopause as end points.

The real value of measuring AMH in young women surviving cancer would be to forecast long-term reproductive outcome and take steps to preserve their fertility.

Reproductive outcomes in adult women
The same fertility concerns exist for women of childbearing age.  Using AMH values to assess ovarian reserve and individualize risk, more invasive methods of fertility preservation may be appropriate for women with a low AMH, while those with high values for their age may decide  to start cancer treatment without delay.

Most evidence comes from breast cancer studies and is based on the assumption that a woman with a higher pre-treatment AMH before chemotherapy will be more likely to retain ovarian function. A prospective study in women with newly diagnosed breast cancer linked high levels of AMH detected before treatment with retaining long-term ovarian function five years after surgery [17]. Pretreatment serum AMH was seen to be markedly higher in women who continued to have menses. The predictive value of AMH for post-chemotherapy ovarian function has subsequently been confirmed [18] allowing the development of prediction tools combining age and AMH [18].

Individualizing breast cancer adjuvant chemotherapy
Adjuvant endocrine therapy has been shown to reduce the likelihood of reocurrence and improve overall survival rates in hormone receptor-positive (HR-positive) breast cancer. However, it appears that ovarian function after chemotherapy has direct implications on the choice of therapy.  Aromatase inhibitors (AIs) are more effective in postmenopausal women than tamoxifen [19]. However, in premenopausal women, AIs may cause a rise in estrogen levels due to reactivation of ovarian function. Consequently, even in women who have developed chemotherapy-induced ovarian failure, tamoxifen is the standard of care [20, 21].

It has been suggested that all women who are premenopausal prior to chemotherapy, even those in their late 40s and early 50s, should be treated with adjuvant tamoxifen therapy or, if they are going to receive an aromatase inhibitor, should have their ovaries removed or chemically suppressed [22]. For the latter group, these strategies are invasive and are associated with increased side effects. Consequently, being able to predict permanent ovarian failure using information other than the patient’s age is relevant.

Data from recent studies [8, 17] suggest that  pre-chemotherapy assessment of serum AMH concentrations, possibly in combination with inhibin B, may provide important information about the likelihood of developing permanent ovarian failure with chemotherapy. In addition, this could help identify a patient population in which it would be safe to treat with upfront AI monotherapy. The expanding number of studies available all add to our understanding of the role of AMH in ovarian function, its ability to predict a woman’s ovarian reserve for her fertility and the impact of cancer treatment on reproductive health.

References
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The author
Sherry Faye, PhD
Director, Global Scientific Affairs,
Beckman Coulter Diagnostics
Brea, CA, USA