Histology using HE-, Ki-67-, and TUNEL-staining of the TUM-CAM model after plasma treatment. Plasma treatment of 10 seconds and 20 seconds (not shown) led to cell death in the upper 3–5 cell layers (above the dotted line), accompanied by a complete absence of viable proliferating cells (Ki-67-staining) and a strong increase in apoptotic activity (TUNEL staining). However, the bottom cell layers were not affected. One mitotic figure (arrow) and a spontaneous apoptotic body (arrowhead) of the unaffected deep layers of a plasma treated tumour as well as an untreated control tumour were marked. The lower edge of HE- and Ki-67-stains measure 250μm (original magnification 400x). Original magnification of TUNEL staining: 200x.