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Intratumor heterogeneity and branched evolution.

To the Editor: Gerlinger et al. (March 8 issue)1 found that the majority of somatic genetic mutations were not present ubiquitously within a tumor, and they report branched evolutionary tumor development in patients with renal cancer. This tumor heterogeneity presents a considerable therapeutic challenge because treatment choices based on a biomarker present in a single biopsy specimen may not be relevant. The increased emphasis on biobanking of tumor tissue in cancer medicine is intended to provide more opportunities for detailed research of tumor biology and identification of therapeutic targets.2 However, biobanks that focus solely on obtaining tissue from primary tumors will not be able to adequately assess tumor heterogeneity. A comparison of primary-tumor tissue with postmortem tumor specimens of metastatic deposits can improve our understanding of tumor heterogeneity by revealing the genetic lesions within a tumor at different points in time and in different areas of the study.3 Furthermore, by examining the metastatic deposits, which ultimately dictate survival, rather than the primary tumor, we can gain an in-depth understanding of the evolution of major driver genetic mutations and drug-resistance mechanisms. Consideration should therefore be given to more widespread development of autopsy-based biobanking in translational research.