Tumor cells identified by positive S100 staining (black arrows, left panel, Figure 1A) expressed clearly detectable amounts of ATF3 (black arrows, right panel, Figure 1A), while melanoma stromal cells identified by their spindle shapes and absence of S100 protein displayed extremely weak ATF3 staining (red arrows, right panel, Figure 1A). The gene discussed is ATF3; the disease is neoplasm.