Identification of Clinically Useful Cancer Prognostic Factors: What Are We Missing?

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Abstract
The number of cancer prognostic markers that have been validated as clinically useful is pitifully small, despite decades of effort and money invested in marker research ( 1 – 3 ) . For nearly all markers, the product has been a collection of studies that are difficult to interpret because of inconsistencies in conclusions or a lack of comparability. Small, underpowered studies; poor study design; varying and sometimes inappropriate statistical analyses; and differences in assay methods or endpoint definitions are but a few of the explanations that have been offered for this disappointing state of affairs ( 4 – 11 ) . Researchers attempting to conduct meta-analyses of prognostic marker studies encounter many difficulties ( 12 – 14 ) . In this issue of the Journal, a meta-analysis by Kyzas et al. ( 15 ) of the tumor suppressor protein TP53 as a prognostic factor in head and neck cancer provides compelling empirical evidence that selective reporting biases are a major impediment to conducting meaningful meta-analyses of prognostic marker studies. These biases have serious implications, not only for meta-analyses but also for interpretation of the cancer prognostic literature as a whole.