Abstract Hypoxia-driven adaptation is a central feature of triple-negative breast cancer (TNBC) and contributes to its aggressive behavior. TNBC lacks ER, PR, and HER2 expression, which limits targeted treatment options. Hypoxia-inducible factors (HIFs), particularly the HIF-1α and HIF-2α isoforms, orchestrate the transcriptional response to low oxygen to maintain survival and metabolic programs, making them attractive therapeutic targets. HIF-1α is the main hypoxic responder in TNBC, but efforts to target it have failed in the clinic. The FDA approval of the HIF-2α inhibitor belzutifan for kidney cancer makes it urgent to determine whether inhibition may be effective in other solid tumors. Although HIF-1α and HIF-2α share some targets, their functions vary by cancer type, and the significance of HIF-2α in TNBC remains unclear. To address this, we investigated the individual and combined contributions of HIF-1α and HIF-2α in TNBC. Here, we show that HIF-2α is an important regulator in TNBC, in part due to previously unrecognized redundant or compensatory interactions between the two isoforms. Dual knockout of HIF-1α and HIF-2α did not further inhibit tumor growth compared to single knockouts, indicating functional overlap. Notably, HIF-2α acted antagonistically to HIF-1α and limited pro-metastatic effects, as HIF-2α knockout tumors showed increased metastatic burden in a syngeneic mouse model. This phenotype was supported by scRNA-seq analysis, which revealed elevated EMT hallmark signatures in HIF-2α-deficient xenograft tumors, and by in vitro observations where HIF-2α-deficient cells displayed a more invasive morphology. Some HIF-2α functions are context-specific and further shaped by the tumor microenvironment. Together, our findings reveal that HIF-1α and HIF-2α engage in redundant, compensatory, or antagonistic interactions dependent on the specific pathway. Thus, both factors contribute to stress responses, but HIF-2α also exhibits cancer-intrinsic functions that may potentially counteract the pro-metastatic effects of HIF-1α. Overall, these findings reveal the nuanced roles of HIF isoforms in tumor progression and highlight the need for careful consideration of HIF-2α targeting in TNBC therapy. Citation Format: Aleksandra K. Kurowska, Long Chi Nguyen, Madeline Henn Bungert, Marsha Rich Rosner. Interplay between HIF-1α and HIF-2α modulates TNBC phenotypes abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 7310.
Kurowska et al. (Fri,) studied this question.