Critical factors in characterizing the aggressiveness and response to therapy for tumors are the availability of noninvasive biomarkers that can be combined with other clinical parameters to tailor treatment regimens to each individual patient. While conventional magnetic resonance (MR) images are widely used to estimate changes in tumor size, they do not provide the rapid readout that is required to make an early decision on whether a change in therapy is required. The use of hyperpolarized (13)C agents to obtain metabolic imaging data is of great interest for in vivo assessment of tumors. One of the first agents being considered for in vivo studies with dynamic nuclear polarization (DNP) is 1-(13)C-labeled pyruvate, which is converted to lactate or alanine, dependent upon the needs of the tissue in question. The development of this new technology and its implementation in preclinical cancer model systems has clearly demonstrated the potential for highlighting tumor aggressiveness and for monitoring changes associated with disease progression. While there is further work to do in terms of studying new agents, improving the DNP process itself and developing efficient MR methods for acquiring and analyzing the data, the preliminary results are extremely promising and provide strong motivation for considering cancer as one of the first applications of the technology.