Pleural fluid marker analysis revealed highly significant differences in the levels of seven of the analysed markers between benign and lung cancer patients (Table 1, Figure 1): the concentrations of all seven markers, MMP-9, MMP-3, CycD1, Ki67, ImAnOx, carbonyls and p27, were lower in cancer patients by 9–65%. This evidence concerns the gene MKI67 and lung cancer.