Endocrine therapies for breast cancer that target the estrogen receptor (ER) are ineffective in the 25%–30% of cases that are ER negative (ER–). Androgen receptor (AR) is expressed in 60%–70% of breast tumors, independent of ER status. How androgens and AR regulate breast cancer growth remains largely unknown. We find that AR is enriched in ER– breast tumors that overexpress HER2. Through analysis of the AR cistrome and androgen-regulated gene expression in ER–/HER2+ breast cancers we find that AR mediates ligand-dependent activation of Wnt and HER2 signaling pathways through direct transcriptional induction of WNT7B and HER3. Specific targeting of AR, Wnt or HER2 signaling impairs androgen-stimulated tumor cell growth suggesting potential therapeutic approaches for ER–/HER2+ breast cancers.