The tumor suppressor menin has dual functions, acting either as a tumor suppressor or as an oncogene/oncoprotein, depending on the oncological context. Triple-negative breast cancer (TNBC) is characterized by lack of expression of the estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 and is often a basal-like breast cancer. TNBC is associated with a dismal prognosis and an insufficient response to chemotherapies. Previously, menin was shown to play a proliferative role in ER-positive breast cancer; however, functions of menin in TNBC remains unknown. We have demonstrated that menin is expressed in various TNBC subtypes with the strongest menin expression in the TNBC Hs 578T cells. Depletion of menin by antisense oligonucleotide inhibited cell proliferation, enhanced apoptosis, and induced cell cycle arrest in Hs 578T cells, highlighting oncogenic functions of menin in this TNBC model. To better understand the menin function, we performed AP-MS (Affinity Purification-Mass Spectrometry) using specific antibody against menin. Analysis of menin interactome suggested that menin could drive TNBC tumorigenesis through regulation of the MLL/KMT2A-driven transcriptional activity, mRNA 3’ end processing and apoptosis.