Role of Monoamine Oxidases in Colorectal cancer: Prognostic implications and therapeutic potential of MAOA and MAOB

Monoamine oxidases (MAOs) are mitochondrial enzymes that degrade monoamines released by neurons and glial cells, thereby regulating cellular signalling and redox balance. Increasing evidence indicates that the two isoforms, MAOA and MAOB, play complex and context-dependent roles in cancer biology, including colorectal cancer (CRC). This review summarizes and critically evaluates current literature and available data on the expression patterns, prognostic significance, and functional roles of MAOA and MAOB in CRC, and contrasts these findings with observations reported in other cancer types. Available studies consistently indicate that reduced MAOA expression in CRC is associated with poor patient prognosis, suggesting a potential protective role of MAOA through modulation of oxidative stress and regulation of oncogenic pathways such as EGFR transactivation. In contrast, elevated MAOA expression has been linked to poor survival outcomes in several other malignancies, underscoring strong cancer-type specificity. MAOB expression in CRC is generally low; however, higher MAOB levels have been associated with worse survival, potentially reflecting tumour heterogeneity, microenvironmental influences, or stage-dependent expression. Collectively, these contrasting patterns highlight the biological complexity and context-dependent functions of MAOs in cancer. The review emphasizes the need for larger, well-characterized clinical cohorts and mechanistic studies to clarify the translational potential of MAOA and MAOB as prognostic biomarkers or therapeutic targets in CRC.