TUNEL assay revealed dense staining (brown) at the site of DNA fragmentation in CEA-Fos-NP PDT xenografts in keeping with significant tumour cell apoptosis (64 ± 2.3%), whilst the controls showed methyl green of normal cells, indicating no tumour apoptosis (2 ± 0.1% for Myo-Fos-NPs, 1.8 ± 0.5% and 1.3 ± 0.3% for PDT-negative controls) (Fig. 6E). The gene discussed is FOS; the disease is neoplasm.