Objective: The purpose of this study was to evaluate the metastatic pattern of muscle-invasive bladder cancer and to correlate the findings with the characteristics of the primary tumor.

Materials and methods: From a clinic population of 392 patients with muscle-invasive (pT2-4) bladder cancer seen at our institution from January 2004 through December 2009, we studied the cases of 150 consecutively registered patients with pathologically proven metastatic disease. The metastasis-free intervals and metastatic patterns of different T categories were compared by Kruskal-Wallis test and Freeman-Halton extension of Fisher's exact test. Patients were divided into two histologic categories, those with transitional cell carcinoma and those with atypical histologic features. The metastasis-free interval and metastatic pattern of these two groups were compared by Mann-Whitney test and Fisher's exact test.

Results: The study group consisted of 150 patients (116 men [77%], 34 women [23%]; median age, 64 years). The transitional cell carcinoma group consisted of 94 (63%) patients and the atypical histologic features group of 56 (37%) patients. The most common metastatic sites were lymph nodes (104 patients, 69%), bone (71 patients, 47%), lung (55 patients, 37%), liver (39 patients, 26%), and peritoneum (24 patients, 16%). Patients with tumors of a more advanced T category had shorter metastasis-free intervals (p = 0.001, df = 2). There was no significant difference in the metastatic patterns of tumors in the different T categories. Patients with atypical histologic features had a shorter median metastasis-free interval (3 months; range, 0-29 months) than patients with transitional cell carcinoma (12 months; range, 0-192 months) (p = 0.0001). Patients with atypical histologic features had a significantly higher incidence of peritoneal metastasis (p < 0.0002).

Conclusion: Lymph nodes, bones, lung, liver, and peritoneum are the most common sites of metastasis from bladder cancer. Tumors in a more advanced T category and those with atypical histologic features metastasize earlier. Tumors with atypical histologic features also have a higher frequency of peritoneal metastasis.