HSD17B7 is a 37 kDa hydroxysteroid dehydrogenase enzyme with dual metabolic roles in steroid and cholesterol biosynthesis 1. Located on chromosome 1 (though earlier studies mapped it to 10p11.2), it catalyzes estrone-to-estradiol conversion and participates in postsqualene cholesterol biosynthesis, with transcriptional regulation dependent on cholesterol levels rather than estradiol in hepatic tissues 2. HSD17B7 is highly expressed in the corpus luteum, placenta, and reproductive tissues 1, and shows marked upregulation in mouse testis under compensatory androgen synthesis conditions 3. During fetal development, HSD17B7 is essential for in situ cholesterol biosynthesis in the developing brain; knockout mice exhibit severe neural and cardiac malformations by day 10.5 of gestation 4. In breast cancer, estradiol stimulates HSD17B7 expression through estrogen receptor-α via an NF1-dependent mechanism, creating a positive feedback loop that promotes local estradiol synthesis and tumor growth 5. Clinically, HSD17B7 expression is significantly elevated in keratinocytes and squamous cell carcinomas from individuals of African ancestry, correlating with increased oncogenic potential and altered mitochondrial function 6. Similarly, elevated HSD17B7 protein expression appears in prostate cancer stroma from African American men, associated with dysregulated estrogen signaling 7. HSD17B7 also shows differential expression in hepatocellular carcinoma 8, suggesting broader involvement in cancer pathogenesis.