Autocrine/paracrine growth hormone in cancer progression

It is now apparent that growth hormone (GH), an anterior pituitary hormone predominantly regulating postnatal somatic growth and metabolism, is also expressed in extrapituitary tissues. An extrapituitary synthetic site of GH that has garnered interest is the de novo or enhanced expression of GH in carcinoma or other cancers. In a number of cancers, including carcinoma of the mammary gland, endometrium, liver, prostate, and colon, the expression of GH is independently associated with more advanced clinicopathologic parameters of the cancer. In some of these cancers, tumor human growth hormone (hGH) expression portends worse survival outcomes for patients. Functionally, tumor-derived hGH exerts both autocrine and paracrine functions on carcinoma cells and cancer-associated stroma. Expression of autocrine/paracrine hGH in cancer drives tumor growth, angiogenesis, metastasis, and resistance to therapy by promotion of cancer cell proliferation, survival, epithelial-to-mesenchymal transition, motility, invasion, cancer stem cell-like behavior, and metastasis. Autocrine/paracrine hGH activates oncogenic signaling pathways and specific transcriptome signatures and enhances the expression of an oncogenic secretome to promote these functions. Hence, extrapituitary expression of GH in cancer promotes cancer progression independent of endocrine hGH, and may be considered as a validated target in oncology.