Biomarkers are changes associated with the disease. Without homeostatic control, urine accumulates very early changes and is an ideal biomarker source. Usually, we performed urinary biomarker studies involving at least thousands of tumor cells. But no tumor starts from a thousand tumor cells. Can we observe any urine proteome changes in rats with approximately ten tumor cells subcutaneous inoculation? Here, we serially diluted Walker-256 carcinosarcoma cells to a concentration of 102/mL and

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... utaneously inoculated 0.1 mL of these cells into nine rats. Urine proteomes on days 0, 13 and 21 were profiled by LC-MS/MS analysis and studied with unsupervised clustering analysis. Samples at three time points were almost clustered together, indicating a good consistency in these nine rats. Differential proteins on days 13 and 21 were mainly associated with cell adhesion, autophagic cell death, changes in extracellular matrix organization, angiogenesis, and the pentose phosphate pathway. All of these enriched functional processes were reported to contribute to tumor progression and could not be enriched through random allocation analysis. Our results indicated that 1) the urine proteome reflects changes associated with cancer even with approximately ten tumor cells in the body and that 2) the urine proteome reflects pathophysiological changes in the body with extremely high sensitivity and provides potential for a very early screening process of clinical patients. Key words: urine, biomarker source, sensitive, proteomics