[en] BACKGROUND: The intensity of the [F]fluorodeoxyglucose (F-FDG) uptake is an independent prognostic indicator in non-small cell lung cancer (NSCLC). We evaluate the relationship between the metabolic activity of the primary and the pleurisy in T4 NSCLC. METHODS: 25 patients (16 males, nine females, mean age 63 years, performance status 1) with pathology-proven, T4 NSCLC and malignant pleurisy were included. All were treated by a platinum salt-based chemotherapy regimen. Positron emission tomography (F-FDG-PET) was performed before treatment, according to a routine procedure. Regions of interest were placed over the primary and the pleural effusion on the transaxial slice showing the highest activity. The maximum pixel standard uptake values (SUVs) were calculated. Overall survival was determined by standard Kaplan-Meier survival analysis. All patients were followed up until death. RESULTS: The median survival for the entire population was 83 days (7-988). The SUVs were higher in the primary than in the pleurisy (9.2+/-5.6 and 5.5+/-2.2, respectively). There was no correlation between primary and pleurisy SUVs (r=0.3, P>0.05). The metabolic activity of the primary tumor did not predict the outcome: the median survival was 77.5 days (range 7-988) and 87 days (19-454) in the groups with SUVs lower and higher than the median value (8.7), respectively (P>0.05). By contrast, the metabolic activity of the pleurisy was significantly correlated with the median survival, which was 196 days (40-988) when the SUVs were lower than the median value (5) and 74 days (7-170) when they were higher (P=0.0096). CONCLUSION: Among patients with T4 NSCLC, those with high metabolic activity in the pleural effusion have a dire prognosis, whereas the metabolic activity of the primary fails to predict the survival.