# Aromatase (CYP19A1)

Source: https://onco.cc/targets/aromatase/  
OnCo record `aromatase` (Target). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

The enzyme that turns androgens into oestrogen in fat, muscle and breast tissue after the menopause. Aromatase inhibitors remove the oestrogen that drives most breast cancers in post-menopausal women.

## Summary

Aromatase, the product of the CYP19A1 gene, converts androstenedione and testosterone into oestrone and oestradiol. After the menopause the ovaries stop making oestrogen and aromatase in peripheral fat, muscle and the breast itself becomes the main source, so inhibiting it with letrozole, anastrozole or exemestane lowers circulating oestrogen to very low levels and deprives hormone receptor-positive breast cancer of its growth signal. Aromatase inhibitors are the standard endocrine partner for CDK4/6 inhibitors in advanced disease and a standard adjuvant treatment in early disease; joint pain and bone loss are their characteristic side effects.

## Fields

- Kind: Target
- Last checked: 2026-09-04
- Symbol: CYP19A1
- Class: enzyme
- Biology: Cytochrome P450 enzyme that aromatises the A ring of androgens to form oestrogens; expressed in adipose tissue, muscle, bone, brain and breast tumour stroma.
- Where found: Hormone receptor-positive breast cancer in post-menopausal women

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Aromatase
- UniProt P11511: CYP19A1: https://www.uniprot.org/uniprotkb/P11511/entry

## Connected records

- cancers: [HR-positive / HER2-negative breast cancer](https://onco.cc/cancers/breast-hr-positive/)
- drugs: [Aminoglutethimide](https://onco.cc/drugs/aminoglutethimide/), [Anastrozole](https://onco.cc/drugs/anastrozole/), [Exemestane](https://onco.cc/drugs/exemestane/), [Formestane](https://onco.cc/drugs/formestane/), [Letrozole (and other aromatase inhibitors)](https://onco.cc/drugs/letrozole/)
- targets: [CYP11A1 (cholesterol side-chain cleavage enzyme)](https://onco.cc/targets/cyp11a1/)

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JSON: https://onco.cc/api/v1/entities/aromatase.json