Histamine and Histaminergic Receptors in Colorectal Cancer: From Basic Science to Evidence-based Medicine

Background: Histamine is an imidazolic compound performing a crucial function in the pathogenesis of inflammation. Several studies have also emphasized its pro-carcinogenic effect in colorectal cancer (CRC). Object: In fact, increased histamine levels have been observed in CRC and a decreased catabolism of this molecule is typical of colorectal adenomas. Additional data have demonstrated that CRC is characterized by an altered balance of histamine receptors (HRs); in fact, HR1 and HR4 are down-regulated in CRC, while HR2 is overexpressed. Method: Based on this evidence, we reviewed several studies investigating the role of HR2 antagonists (HR2A), such as cimetidine in CRC. Results: From a clinical point of view, HR2A may prolong the survival rates of patients with CRC, and a recent meta-analysis seems to confirm this finding. From a biological perspective, it has been demonstrated that HR2A could have a beneficial effect on CRC for many reasons: i) promotion of peri-tumoral lymphocyte growth and improvement of immune response against the tumor, ii) suppression of adhesion molecules which might favor metastasis, iii) anti-angiogenetic activity (reduction of VEGF), iv) increased production of some cytokines which may counteract tumor growth, such as tumor necrosis factor (TNF) alpha, interleukin (IL)-10 and IL-15. On the contrary, HR1 antagonists did not demonstrate any beneficial effect on CRC. Therefore, it is presumable that histamine could be a relevant player in the development of CRC, but its effect might be mediated by an imperfect homeostasis of its receptors. Conclusion: In this scenario, HR2A could inhibit carcinogenesis whereas HR2 might act as a pro-carcinogenetic, while HR1 and HR4, being suppressed in CRC, may antagonize neoplastic development.