# 5-alpha-reductase type 2 (SRD5A2)

Source: https://onco.cc/targets/srd5a2/  
OnCo record `srd5a2` (Target). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

5-alpha-reductase turns testosterone into the more potent dihydrotestosterone inside the prostate; finasteride and dutasteride block it, and two large trials showed they cut prostate cancer diagnoses by about a quarter while raising concern about high-grade tumours.

## Summary

Steroid 5-alpha-reductase type 2 converts testosterone to dihydrotestosterone, the androgen that drives prostate growth. Finasteride (type 2 selective) and dutasteride (types 1 and 2) are approved for benign prostatic enlargement and were tested for prevention in the Prostate Cancer Prevention Trial and the REDUCE trial, where they reduced the overall incidence of prostate cancer but were associated with a small excess of high-grade cancers, so neither is approved for prevention. In castration-resistant prostate cancer, tumour cells raise their own 5-alpha-reductase and other steroidogenic enzymes to make androgens, part of the rationale for abiraterone and the newer androgen receptor blockers.

## Fields

- Kind: Target
- Last checked: 2026-09-04
- Tags: chembl-gap
- Symbol: SRD5A2
- Class: enzyme
- Biology: A membrane enzyme of the endoplasmic reticulum in prostate, genital skin and hair follicles; it is NADPH-dependent and genetic loss causes a disorder of sex development.
- Where found: Prostate epithelium and stroma; Castration-resistant prostate cancer cells making their own androgens

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/3-oxo-5α-steroid_4-dehydrogenase
- UniProt P31213: SRD5A2: https://www.uniprot.org/uniprotkb/P31213/entry
- HGNC:11285 SRD5A2: https://www.genenames.org/data/gene-symbol-report/#!/hgnc_id/HGNC:11285
- ChEMBL target CHEMBL1856: https://www.ebi.ac.uk/chembl/explore/target/CHEMBL1856

## Connected records

- targets: [Androgen receptor](https://onco.cc/targets/androgen-receptor/), [CYP17A1 (17-alpha-hydroxylase/17,20-lyase)](https://onco.cc/targets/cyp17a1/)
- cancers: [Prostate cancer](https://onco.cc/cancers/prostate/)
- drugs: [Abiraterone acetate](https://onco.cc/drugs/abiraterone/)

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JSON: https://onco.cc/api/v1/entities/srd5a2.json