1 Department of Gastroenterological Surgery (Surgery II), Nagoya University Graduate School of Medicine, Nagoya, Japan2 Department of Biostatistics, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan3 Department of Surgery, Yokohama City University, Yokohama, Japan4 Department of Surgery, Keio University School of Medicine, Tokyo, Japan5 Cancer Treatment Center, Kochi Medical School Hospital, Kochi, Japan6 Department of Minimally Invasive Surgical and Medical Oncology, Fukushima Medical University, Fukushima, Japan7 Faculty of Engineering, Tokyo University of Science, Tokyo, Japan8 Department of Surgery, Tokai University, Isehara, Japan9 Tokai Central Hospital, Kakamigahara, Japan10 Japanese Foundation for Multidisciplinary Treatment of Cancer, Tokyo, Japan11 Department of Gastrointestinal Surgery, Kanagawa Cancer Center, Yokohama, Japan
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BACKGROUND:Although colorectal cancer comprises several histological subtypes, the influences of histological subtypes on disease progression and treatment responses remain controversial.OBJECTIVE:We sought to evaluate the prognostic relevance of mucinous and poorly differentiated histological subtypes of colorectal cancer by the propensity score weighting analysis of prospectively collected data from multi-institute phase III trials.DESIGN:Independent patient data analysis of a pooled database from 3 phase III trials was performed.SETTINGS:An integrated database of 3 multicenter prospective clinical trials (the Japanese Foundation for Multidisciplinary Treatment of Cancer 7, 15, and 33) was the source of study data.INTERVENTIONS:Surgery alone or postoperative adjuvant chemotherapy was offered in patients with resectable colorectal cancer.MAIN OUTCOME MEASURES:To balance essential variables more strictly for the comparison analyses, propensity score weighting was conducted with the use of a multinomial logistic regression model. We evaluated the clinical signatures of mucinous and poorly differentiated subtypes with regard to postoperative survival, recurrence, and chemosensitivity.RESULTS:Of 5489 patients, 136 (2.5%) and 155 (2.8%) were pathologically diagnosed with poorly differentiated and mucinous subtypes. The poorly differentiated subtypes were associated with a poorer prognosis than the “others” group (HR, 1.69; 95% CI, 1.00–2.87; p = 0.051), particularly in the patient subgroup of adjuvant chemotherapy (HR, 2.16). Although the mucinous subtype had a marginal prognostic impact among patients with stage I to III colorectal cancer (HR, 1.33; 95% CI, 0.90–1.96), it was found to be an independent prognostic factor in the subpopulation of patients with stage II disease, being associated with a higher prevalence of peritoneal recurrence.LIMITATIONS:The treatment regimens of postoperative chemotherapy are now somewhat outdated.CONCLUSIONS:Both mucinous and poorly differentiated subtypes have distinct clinical characteristics. Patients with the mucinous subtype require special attention during follow-up, even for stage II disease, because of the risk of peritoneal or local recurrence. See Video Abstract at http://links.lww.com/DCR/A531.