# CYP17A1 (17-alpha-hydroxylase/17,20-lyase)

Source: https://onco.cc/targets/cyp17a1/  
OnCo record `cyp17a1` (Target). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

The enzyme that makes androgens in the testes, the adrenal glands and prostate tumours themselves. Abiraterone blocks it, cutting androgen production below what castration alone achieves.

## Summary

CYP17A1 catalyses two steps, 17-alpha-hydroxylation and 17,20-lyase cleavage, that convert pregnenolone and progesterone into DHEA and androstenedione, the precursors of testosterone and dihydrotestosterone. Because castration-resistant prostate cancer keeps making androgens from adrenal precursors and inside the tumour, blocking CYP17A1 with abiraterone lowers androgens further than castration and restores control in many patients. Blocking the enzyme also diverts steroid synthesis towards mineralocorticoids, which is why abiraterone is given with prednisone or prednisolone.

## Fields

- Kind: Target
- Last checked: 2026-09-04
- Symbol: CYP17A1
- Class: enzyme
- Biology: Cytochrome P450 enzyme of the adrenal cortex, testis and prostate cancer cells; the rate-limiting step of androgen synthesis from pregnenolone.
- Where found: Prostate cancer, including intratumoral androgen synthesis in castration-resistant disease

## Notes

- Prostate cancer: the reason the AR L702H allele matters. L702H makes the receptor responsive to glucocorticoid, and abiraterone, a CYP17A1 inhibitor, is given with prednisone or prednisolone to offset mineralocorticoid excess, so the steroid given with the drug can in principle feed a receptor carrying that allele.

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/CYP17A1
- UniProt P05093: CYP17A1: https://www.uniprot.org/uniprotkb/P05093/entry

## Connected records

- targets: [5-alpha-reductase type 2 (SRD5A2)](https://onco.cc/targets/srd5a2/), [Androgen receptor](https://onco.cc/targets/androgen-receptor/), [CYP11A1 (cholesterol side-chain cleavage enzyme)](https://onco.cc/targets/cyp11a1/)
- cancers: [Metastatic castration-resistant prostate cancer](https://onco.cc/cancers/prostate-mcrpc/), [Prostate cancer](https://onco.cc/cancers/prostate/)
- drugs: [Abiraterone acetate](https://onco.cc/drugs/abiraterone/), [Galeterone](https://onco.cc/drugs/galeterone/), [Orteronel](https://onco.cc/drugs/orteronel/)
- terms: [Castration-resistant prostate cancer (CRPC)](https://onco.cc/terms/castration-resistance/), [mCRPC and mHSPC (castration-resistant vs hormone-sensitive prostate cancer)](https://onco.cc/terms/mcrpc-mhspc/)
- key papers: [Mutation of the androgen-receptor gene in metastatic androgen-independent prostate cancer](https://onco.cc/key-papers/paper-taplin-ar-mutation-androgen-independent-prostate-nejm-1995/)
- trials: [ARMOR3-SV](https://onco.cc/trials/armor3-sv/), [ELM-PC 4](https://onco.cc/trials/elm-pc-4-orteronel/)
- biomarkers: [AR ligand-binding-domain mutation (L702H, W742C, H875Y, T878A, F877L)](https://onco.cc/biomarkers/ar-ligand-binding-domain-mutation/)

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