en Cancer Cancer Original Article Original Article <p style="text-align: justify;"><span style="font-size:12px;"><span style="font-family:Tahoma;"><span style="line-height:14.0pt">Although mucin-producing carcinomas of the gastrointestinal tract and breast have similar histological characteristics, their clinical behavior and prognosis vary. The relationship of mucin gene product expression in the development of these clinical differences is poorly understood. This study examines the histopathological characteristics of gastrointestinal and breast mucin-producing carcinomas for the expression of MUC1, MUC2, MUC4, and MUC5AC and their relationship to patient outcome. A retrospective comparative study of 120 mucinous carcinomas of the gastrointestinal tract and breast (60 in each group) was conducted. The histopathological characteristics of the tumors were examined.<b> </b>MUC gene expression was quantified by RT-qPCR in a subset of 60 cases. Overall survival was evaluated in the RT-qPCR subset using Kaplan&ndash;Meier analysis and multivariate Cox proportional hazards models. Gastrointestinal tumors exhibited significantly higher histologic grade and greater necrosis compared with mammary tumors (<i>P</i> < 0.01). MUC2 and MUC5AC were markedly overexpressed in gastrointestinal carcinomas (<i>P</i> < 0.001 for both), whereas MUC1 and MUC4 were expressed across both tumor types. In multivariate analysis, high expression of MUC1 (hazard ratio = 2.18; 95% confidence interval [CI], 1.31&ndash;3.61; <i>P</i> = 0.003) and MUC4 (HR = 1.89; 95% CI, 1.10&ndash;3.23; <i>P</i> = 0.017) was independently associated with reduced overall survival. In contrast, MUC2 and MUC5AC expression distinguished tumor origin but showed no prognostic significance (<i>P</i> > 0.05). Mucin gene expression profiles differ substantially between GI and mammary mucin-rich carcinomas. MUC1 and MUC4 have prognostic relevance, while MUC2 and MUC5AC aid in determining tumor origin. Integrating histopathological evaluation with molecular profiling may improve diagnostic accuracy and risk stratification in mucin-rich carcinomas.</span></span></span></p> Mucinous carcinoma, Gastrointestinal tumours, Breast tumours, Gene expression, Prognostic biomarkers, Histopathology 1216 1227 http://ijmcmed.org/browse.php?a_code=A-10-9079-1&slc_lang=en&sid=1 Mahmoud Mohammed Mahmoud mohammed3m@proton.me 100319475328460037128 100319475328460037128 Yes Department of Pathology, College of Medicine, University of Kirkuk, Kirkuk, Iraq Mohanad Mundher Abdulghani Baghdad.mohanedmonther@kmc.uobaghdad.edu.iq 100319475328460037129 100319475328460037129 No Department of Pathology and Forensic Medicine, Al Kindy College of Medicine, University of Baghdad, Iraq Dler Omar Mohammed drdler1974@uokirkuk.edu.iq 100319475328460037130 0002-0002-9483-9717 No Department of General Surgery, College of Medicine, University of Kirkuk, Kirkuk, Iraq.