To our knowledge, only MMP-2 and MMP-9 were previously analysed in the pleural fluid of lung cancer and benign inflammatory patients (Kotyza et al, 2004; Di Carlo et al, 2005, 2007; Iglesias et al, 2005; Park et al, 2005; Vatansever et al, 2009). Here, MMP2 is linked to lung cancer.