Background The number of metastatic lesions is closely correlated with prognosis in most cancers. The aim of this study was to clarify the relationship between individual heterogeneity of metastatic tumor sizes and prognosis in patients with multiple pulmonary metastasis of colorectal cancer who received surgical treatment. Methods Clinical data for patients who had pulmonary metastasis from colorectal cancer and underwent curative resection at 46 Japanese institutions between January 2004 and December 2008 were collected. Among 898 patients eligible considering these inclusion criteria, 247 patients had multiple metastases and were analyzed. A difference between the maximum and minimum tumor diameters (Dmax-min) on pathologic findings was used to evaluate size heterogeneity. Results The overall survival rate was 75% at 3 years and 58% at 5 years, with a median follow-up period of 65 months (range, 0 to 112). When Dmax-min of 5 mm was set as a cutoff value, overall survival was significantly different between small (≤5 mm, n = 95) and large (>5 mm, n = 152) tumor groups (5-year survival rates, 66.5% and 53.3%, respectively; log rank test, p = 0.025). Multivariate analysis using a Cox proportional hazards model revealed that disease-free interval from resection of primary lesion, serum carcinoembryonic antigen level, number of pulmonary metastases, and Dmax-min were independent prognostic factors. Conclusions The heterogeneity of metastatic tumor sizes may be an indicator for prognosis in patients with multiple pulmonary metastases of colorectal cancer who underwent resection.
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