Many of the filters are statistical in nature, as- sessing the relative performance of candidate markers on relatively small, "convenience" sample sets that are themselves subject to experimental bias and con- founding factors. ...an imperative next step is the reproduction of the original result on a com- pletely independent sample set, which is presumed to have an independent set of potential confounders (8 ). Recent technical advances in both mass spectrometry platforms and in work flows for targeted mass spectrometry analyses, enabling detection and quantification at less than 1 ng/mL (13, 14), suggest that investigators might soon be able to proceed through the initial verification and preclinical validation phases without the requirement for antibody development, thus focusing antibody development only on those targets worth pursuing and additionally increasing the return on investment for highly rigorous antibody development efforts.