Forkhead Box P1 (FOXP1) is a member of the FOX family of transcription factors. FoxP1 has been implicated in cardiac, lung, and lymphocyte development. FoxP1 knock out mice die at embryonic day 14.5 due to heart valve and outflow tract abnormalities. FoxP1 contains both a DNA binding domain as well as protein-protein interaction domains. FoxP1 can homo or heterodimeize with FoxP2 and FoxP4, with dimerization necessary for DNA binding. FoxP1 shows both oncogenic and tumor suppressive characteristics. Overexpression in lymphomas leads to poor prognosis, whereas, loss of FoxP1 in breast cancer also implicates a poor prognosis.