title: Effect of M1a and M1b category in metastatic colorectal cancer.
abstract: BACKGROUND
  In 2009, the American Joint Committee on Cancer version 7 staging system introduced the M1 subclassifications M1a (single metastatic site) and M1b (peritoneal or multiple metastatic sites). The study objectives were to evaluate the prognostic effect of site of metastasis and M1a/b category among patients with newly diagnosed colorectal cancer and synchronous metastasis.
  
  
  METHODS
  Patients with newly diagnosed pathologic or clinical category M1 colorectal cancer referred to the British Columbia Cancer Agency between 1999 and 2007 were included. Demographic, tumor, treatment, and outcome data were prospectively collected, and prognostic factors were identified. Univariate Cox models were used to assess the prognostic impact of individual sites of metastasis and to determine the effect of M1a/b category on overall survival (OS).
  
  
  RESULTS
  Among 2,049 eligible patients, 70% had M1a and 30% M1b category disease. The most common sites of common single sites of metastasis included liver (56%), lung (5.3%), and peritoneum (3.6%). Metastasis to a single organ or site, including peritoneum, was associated with improved OS compared with multiple sites of metastasis. In multivariate analysis, M1b category conferred inferior survival and hazard ratio (HR) 1.38 (95% confidence interval [CI]: 1.22, 1.55), along with age >70 and Eastern Cooperative Oncology Group performance status of 3-4. Resection of primary tumor was associated with improved survival, HR 0.46 (95% CI: 0.41, 0.52). Results were similar in subgroup analysis of patients undergoing resection of their primary tumor when histology, tumor, and node category were included.
  
  
  CONCLUSIONS
  The results lend support to the introduction of M1a/b colorectal cancer categories. Consideration may be given to classifying patients with solitary peritoneal metastasis only as M1a rather than M1b category. Further refinement of category M1a to reflect resectability of metastasis at initial diagnosis may improve prognostication.
authors.affiliation: Division of Medical Oncology, British Columbia Cancer Agency, Vancouver, British Columbia, Canada; Division of Medical Oncology, Juravinski Cancer Centre, McMaster University, Hamilton, Ontario, Canada; Division of Medical Oncology, Knight Cancer Institute and Oregon Health Science University, Portland, Oregon, USA; Breast and Gastrointestinal Cancer Outcomes Unit, Cancer Surveillance & Outcomes, and Cancer Control Research, British Columbia Cancer Agency, Vancouver, British Columbia, Canada hkennecke@bccancer.bc.ca.
authors.forename: Hagen
authors.initials: H
authors.lastname: Kennecke
authors.affiliation: Division of Medical Oncology, British Columbia Cancer Agency, Vancouver, British Columbia, Canada; Division of Medical Oncology, Juravinski Cancer Centre, McMaster University, Hamilton, Ontario, Canada; Division of Medical Oncology, Knight Cancer Institute and Oregon Health Science University, Portland, Oregon, USA; Breast and Gastrointestinal Cancer Outcomes Unit, Cancer Surveillance & Outcomes, and Cancer Control Research, British Columbia Cancer Agency, Vancouver, British Columbia, Canada.
authors.forename: Jason
authors.initials: J
authors.lastname: Yu
authors.affiliation: Division of Medical Oncology, British Columbia Cancer Agency, Vancouver, British Columbia, Canada; Division of Medical Oncology, Juravinski Cancer Centre, McMaster University, Hamilton, Ontario, Canada; Division of Medical Oncology, Knight Cancer Institute and Oregon Health Science University, Portland, Oregon, USA; Breast and Gastrointestinal Cancer Outcomes Unit, Cancer Surveillance & Outcomes, and Cancer Control Research, British Columbia Cancer Agency, Vancouver, British Columbia, Canada.
authors.forename: Sharlene
authors.initials: S
authors.lastname: Gill
authors.affiliation: Division of Medical Oncology, British Columbia Cancer Agency, Vancouver, British Columbia, Canada; Division of Medical Oncology, Juravinski Cancer Centre, McMaster University, Hamilton, Ontario, Canada; Division of Medical Oncology, Knight Cancer Institute and Oregon Health Science University, Portland, Oregon, USA; Breast and Gastrointestinal Cancer Outcomes Unit, Cancer Surveillance & Outcomes, and Cancer Control Research, British Columbia Cancer Agency, Vancouver, British Columbia, Canada.
authors.forename: Winson Y
authors.initials: WY
authors.lastname: Cheung
authors.affiliation: Division of Medical Oncology, British Columbia Cancer Agency, Vancouver, British Columbia, Canada; Division of Medical Oncology, Juravinski Cancer Centre, McMaster University, Hamilton, Ontario, Canada; Division of Medical Oncology, Knight Cancer Institute and Oregon Health Science University, Portland, Oregon, USA; Breast and Gastrointestinal Cancer Outcomes Unit, Cancer Surveillance & Outcomes, and Cancer Control Research, British Columbia Cancer Agency, Vancouver, British Columbia, Canada.
authors.forename: Charles D
authors.initials: CD
authors.lastname: Blanke
authors.affiliation: Division of Medical Oncology, British Columbia Cancer Agency, Vancouver, British Columbia, Canada; Division of Medical Oncology, Juravinski Cancer Centre, McMaster University, Hamilton, Ontario, Canada; Division of Medical Oncology, Knight Cancer Institute and Oregon Health Science University, Portland, Oregon, USA; Breast and Gastrointestinal Cancer Outcomes Unit, Cancer Surveillance & Outcomes, and Cancer Control Research, British Columbia Cancer Agency, Vancouver, British Columbia, Canada.
authors.forename: Caroline
authors.initials: C
authors.lastname: Speers
authors.affiliation: Division of Medical Oncology, British Columbia Cancer Agency, Vancouver, British Columbia, Canada; Division of Medical Oncology, Juravinski Cancer Centre, McMaster University, Hamilton, Ontario, Canada; Division of Medical Oncology, Knight Cancer Institute and Oregon Health Science University, Portland, Oregon, USA; Breast and Gastrointestinal Cancer Outcomes Unit, Cancer Surveillance & Outcomes, and Cancer Control Research, British Columbia Cancer Agency, Vancouver, British Columbia, Canada.
authors.forename: Ryan
authors.initials: R
authors.lastname: Woods
mesh_terms: D000368:Aged; D015179:Colorectal Neoplasms / Q000473:pathology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D009362:Neoplasm Metastasis; D009367:Neoplasm Staging; D011379:Prognosis; D016016:Proportional Hazards Models; D011446:Prospective Studies; D016019:Survival Analysis
keywords: M1a; M1b; Metastatic colorectal cancer; Prognostic factors