Pleural fluids associated with metastatic lung tumors are rich in progelatinase B/proMMP-9.

Gelatinase B/MMP-9 is a member of matrix metalloproteinases with a major role in extracellular matrix degradation, cell proliferation and migration. Its proenzyme form has also been reported in pleural fluids as an inducible species, but its relation to pleural pathology has not yet been fully clarified. The primary goal of this study was to evaluate proMMP-9 as a potential marker for differentiating pleural effusions of both malignant and non-malignant origin. Pleural fluid samples were studied from 194 patients, including tumor etiology in 133 cases, inflammatory disorders in 33, transudates in 12, and unspecified disorders in 16 patients. The concentrations of proMMP-9 were estimated by means of immunoassays and/or by scanning zymography. Samples were also examined for C-reactive protein (CRP). The analysis of proMMP-9 showed significant differences among the etiological groups with the highest concentrations in para-inflammatory exudates, intermediate in para-neoplastic exudates, and the lowest in transudates. However, the analysis of the para-neoplastic group revealed a distinct heterogeneity with a minor portion of fluids reaching values typical for para-inflammatory effusions. A subsequent sorting based on tumor histology showed increased levels particularly in exudates associated with metastatic tumors. Interestingly, proMMP-9 values in general correlated with CRP, a systemic marker of inflammation. Thus, MMP-9 proenzyme appears to complement traditional markers distinguishing pleural fluids of different origin. Yet, the differentiation between paraneoplastic and para-inflammatory exudates must be regarded with caution due to the presence of a high-expressive paraneoplastic sub-population, including effusions associated with metastatic tumors.