Intratumoral androstene-3,17-dione defines breast cancer subtype and prognosis.

Androgens inhibit breast cancer (BC) growth in estrogen receptor (ER)-positive BC and promote growth in ER-negative BC. Correlating intratumoral androgens, instead of circulating androgens, and their downstream transcriptome, a measure of free unbound androgen function, may offer a direct assessment of androgen action in BC. Intratumoral androgen androstenedione (A4) levels in BC specimens correlated with 1388 genes, which classified patients into low, intermediate, and high A4 levels. This A4-high patients' transcriptome was associated with lower tumor cell proliferation, earlier stage and grade, and longer survival, while A4-low patients' transcriptome was associated with the triple-negative subtype. We developed a 90-gene A4-associated transcriptional classifier that captures intratumoral A4-associated biology. The signature requires independent validation. snRNAseq analysis indicated that high A4 specimens were enriched for favorable cell lineage, while low A4 specimens were enriched for aggressive cell lineage and cancer hallmarks. Supporting in vitro evidence suggests that A4 can inhibit ER-positive AR-positive BC cells. Collectively, these data show that intratumoral A4 levels are associated with a transcriptional state linked to lower proliferation, more luminal features, and better BC outcome.