Predictive accuracy of the metastatic signature decreases for samples with low tumor percentage. (a) Predictive accuracy of the metastatic HNSCC signature per tumor percentage group. The predictive accuracy is expressed as the percentage of samples for which the previously published 120-gene primary tumor signature  correctly determined the absence or presence of metastasis based on comparison with histological examination of surgically removed neck lymph tissue. Signature outcome for samples with a tumor percentage of (b) 50% or less, (c) between 60% and 70% and (d) 80% or more. A signature outcome less than zero indicates a metastatic (N+) profile and an outcome above zero indicates a non-metastatic (N0) outcome. Solid circles indicate tumor samples from patients with metastasis; open circles indicate tumor samples from patients without metastasis.