Atamestane
An investigational oral steroidal (type I) aromatase inhibitor studied for breast cancer, sometimes in combination with the SERM toremifene. It irreversibly inhibits aromatase but never reached broad market approval.
01 Overview
Atamestane is a steroidal, mechanism-based aromatase inhibitor evaluated for hormone-receptor-positive breast cancer, including a large phase III trial combining it with toremifene versus letrozole. The combination did not prove superior, and the drug was not brought to market.
It is chemically related to methyltestosterone-type steroids and irreversibly inactivates aromatase. Human data are limited relative to the marketed third-generation inhibitors, so its research score is moderate.
02 Mechanism
Steroidal (type I) suicide-substrate aromatase inhibitor: binds and irreversibly inactivates aromatase, lowering estradiol.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Trial dose | 500–1000 mg/day | Oral | Dosing used in breast cancer studies. |
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Estradiol suppressionIrreversible aromatase inactivation lowers circulating oestrogen. | Significant estradiol reduction | Clinical | |
| Reduced estrogenic side effectsLower estradiol reduces water retention and breast tissue stimulation in androgen users. | Less bloat / gyno risk | Observational |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| Estrogen deficiency symptomsArthralgia and low libido from suppressed oestrogen. | Moderate | Common | Clinical | |
| Adverse lipid changesReduced oestrogen can worsen HDL and cardiovascular risk markers. | Moderate | Uncommon | Observational |