Verifying the M1c category of CRC: analysis of the data from a Japanese multi-institutional database

  • Toshimichi Tanaka
  • Heita OzawaEmail author
  • Yusuke Nakagawa
  • Akira Hirata
  • Shin Fujita
  • Kenichi Sugihara
Original Article



In the TNM classification 8th edition, colorectal cancer (CRC) with peritoneal metastasis, one of the most poor prognostic factors, is classified as M1c (stage IVC), regardless of the presence/absence of other distant metastasis. Several cases with peritoneal metastasis have been successfully managed by surgical treatment; therefore, there is need to give more consideration for uniform differentiation of peritoneal metastasis. This study was aimed at verifying the classification of M1c in CRC.

Materials and methods

Data from a multi-institutional retrospective cohort of 2929 CRC patients who were diagnosed as having stage IV CRC from 1997 to 2007 were analyzed. Peritoneal metastasis alone was defined as M1c1 and peritoneal metastasis with other organ metastasis was defined as M1c2.


The 3-year OS of patients with M1c1 was significantly higher than that of patients with M1b (25.6% vs. 18.1%; HR 0.77; 95% confidence interval (CI) 0.65–0.92; p = 0.005); in particular, the prognosis of patients with M1c1 with localized peritoneal metastasis and R0 resection was equivalent to that of patients with M1a (3-year OS 40.5% vs. 39.2%, p = 0.41). On the other hand, among the stage IV cases, patients with M1c2 had a low R0 resection rate (5.9%) and the worst prognosis (3-year OS, 9.1%).


The prognosis of M1c1 with localized peritoneal metastasis is relatively good, and can be further improved by surgical intervention. Combined evaluation of the M1c1/2 classification with the peritoneal metastasis grade may help in establishing more individualized treatment strategies.


Colorectal cancer Peritoneal metastasis TNM staging system Stage IVC 



The authors completed this study in collaboration with the following: M. Watanabe (Kitasato University School of Medicine), I. Takemasa (Sapporo Medical University), K. Hakamada (Hirosaki University), H. Kameyama (Niigata University), H. Ueno (National Defense Medical college), S. Ishihara (Tokyo University), K. Takahashi (Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital), Y. Kanemitsu (National Cancer Center Hospital), M. Itabashi (Tokyo Women’s Medical University), T. Kiyomatsu (National Center for Global Health and Medicine), Y. Kinugasa (Tokyo Medical and Dental University), K. Okabayashi (Keio University), Y. Hashiguchi (Teikyo University), T. Masaki (Kyorin University), K. Hanai (Fujita Health University), K. Komori (Aichi Cancer Center Hospital), Y. Sakai (Kyoto University), M. Ohue (Osaka Medical Center for Cancer and Cardiovascular Diseases), N. Tomita (Hyogo College of Medicine), and Y. Akagi (Kurume University).

Compliance with ethical standards

This study was conducted in accordance with the Declaration of Helsinki and with the approval of the Research Ethics Committee of Tochigi Cancer Center. Informed consent for this research was substituted by a consent form at each of the participant’s institutes, because of the retrospective study design.

Conflict of interest

The authors declare that they have no conflict of interest.

Ethical statement

Ethics approval was obtained from the Tochigi Cancer Center’s institutional review board, and for this type of study, formal consent is not required.


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Department of SurgeryTochigi Cancer CenterTochigiJapan
  2. 2.Tokyo Medical and Dental UniversityTokyoJapan

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