<b/> Characterization of intratumoral leukocyte populations may help in estimating patients' prognosis and predictions. A new study shows remarkable differences between the <i>in situ</i> and invasive breast cancer stages and highlights that cell number analyses should be complemented with characterization of T-cell functions, increasing the likelihood that immune competent antitumor T cells and further biomarkers are identified for guiding therapy choices. <i>Cancer Discov; 7(10); 1062-4. ©2017 AACR.</i> <i>See related article by Gil Del Alcazar et al., p. 1098</i> .