Exploring the role of the tumor microenvironment in refractory pituitary tumor pathogenesis

Purpose: Treatment-refractory pituitary tumors demonstrate characteristics resembling those of highly aggressive tumors, in which the local tumor microenvironment (TME) plays a dominant role in promoting aggressiveness and refractoriness. However, role of the TME in pituitary tumors is not well studied.

Methods: Literature on the TME and development of refractory pituitary tumors was reviewed RESULTS: TME harbors tumorigenic immune cells, cancer-associated fibroblasts (CAF), extracellular matrix, and other factors that have been shown to affect behavior of tumor tissue. For example, tumor-associated macrophages and tumor-infiltrating lymphocytes correlate with aggressive and invasive tumor behavior in nonfunctioning and growth hormone-secreting (GH) pituitary tumors, while CAF release of TGFβ, FGF2, cytokines, chemokines, and growth factors may promote treatment resistance, tumor fibrosis, and inflammation in prolactinomas and GH-secreting tumors. In turn, Wnt pathway activation can further promote cell growth in dopamine-resistant prolactinomas. Finally, proteins secreted by extracellular matrix are associated with increased angiogenesis in invasive tumors.

Conclusion: It is likely that multiple mechanisms, including TME, contribute to the development of aggressive refractory pituitary tumors. Given the increased morbidity and mortality associated with pituitary tumor refractoriness, more research on the role of TME is warranted.