Triple negative breast cancer (TNBC) is an aggressive breast cancer subtype for which no effective targeted therapies are available. Growing evidence suggests that cancer cells with stem-like properties (CSC) may repopulate the tumor. One of the approaches that are getting great attention in treating the disease is to modulate the immune system of the patient. In TNBC, the expression of transcription factor RUNX1 correlates with poor prognosis. We identified that RUNX1 is relevant in tumor aggressiveness in TNBC cell models, for the regulation of oncogenes, cell migration and drug resistance. On the other hand, the transcription factor KLF4 is required to generate CSCs in TNBC. In addition, PD-L1 plays a crucial role in TNBC as it facilitates tumor cells to evade the immune response. Both KLF4 and PD-L1 have been described as RUNX1 target genes in other tumors. Our goal was to investigate the regulation of KLF4 and PD-L1 by RUNX1 in TNBC cell lines. To consider intratumor heterogeneity we used two cell culture models: attached and forced suspension (CSC-like). To inhibit RUNX1 transcriptional activity we used the commercial inhibitor AI-10-104. We found that when RUNX1 activity is inhibited in attached MDA-MB-231 and -468 cell lines KLF4 levels are increased, in a dose- and time-dependent manner (p<0.05). Growing MDA-MB-468 in forced-suspension significantly increased KLF4 and RUNX1 levels. Interestingly, under forced suspension conditions, KLF4 levels were notably reduced when RUNX1 was inhibited. Finally, by flow cytometry, we found that PD-L1 is strongly downregulated in the attached MDA-MB-231 treated with AI-10-104. Taken together, these results suggest that RUNX1 may act antagonistically in tumor intra heterogeneity and may contribute to immune evasion of TNBC. The characterization of this dual gene regulation within the intratumoral cell variation is crucial for the development of future therapeutic strategies.