Endometriotic implants retain the capacity for local oestradiol synthesis despite systemic progestin therapy. Which enzyme expressed within endometriotic stromal cells forms the biochemical basis for using aromatase inhibitors such as letrozole in refractory disease?

• A 17-beta-hydroxysteroid dehydrogenase type 2
• B Aromatase (CYP19A1) ✓
• C 5-alpha reductase
• D Cholesterol side-chain cleavage enzyme

Explanation

Eutopic endometrium normally inactivates oestradiol via 17-beta-HSD type 2, but endometriotic tissue aberrantly expresses aromatase (CYP19B1), converting adrenal androgens to oestradiol locally and sustaining lesion growth. Letrozole blocks this final step of oestrogen synthesis, hence its use as add-back or second-line therapy. 5-alpha reductase generates dihydrotestosterone, and side-chain cleavage enzyme acts earlier in steroidogenesis in the adrenal cortex and gonads.

Reference: Williams Gynecology, 4th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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