Estimation of the malignancy of pleural effusions by electron spin resonance

We conducted an electron spin resonance (ESR) study on human pleural effusions obtained from patients (n = 15) with and without cancer at 77 K. We detected two kinds of signals which are considered to be due to transition metal ions in metalloproteins such as Fe3+ in transferrin and Cu2+ in ceruloplasmin from their g values (g = 4.2 and 2.049) and line shapes. We found a significant difference in the signal intensity ratio, Cu2+/Fe3+, of the pleural effusions between cancer and noncancer patients by the Mann-Whitney U test (P < 0.01). The ESR study of pleural effusion enabled us to estimate its malignancy and may have future applications.