Interleukin-33 (IL-33) is a member of the IL-1 cytokine family, primarily known as a mediator of the humoral immune response. It provides protection of barrier tissues and participates in the development of a range of diseases. This cytokine promotes carcinogenesis by induction of proliferation and survival of cancer cells, remodeling of the tumor microenvironment, and promoting immunosuppressive conditions. Elevated levels of IL-33 were observed in many types of cancers. This elevation correlates with a poor prognosis, making IL33 a promising target for cancer immunotherapy. The mechanisms of IL-33 expression regulation in human tumor cells are not well understood. Here, we show that that expression of IL-33 in breast and lung cancer cell lines depends, at least in part, on the activity of the SP1 and FOXA1 transcription factors. Increases in the activity of these transcription factors may be responsible for elevated levels of IL-33 and subsequent tumor progression.