pulmonary mucoepidermoid carcinoma ( pmec ) is a rare cancer that comprises only 0.1 to 0.2% of all primary lung malignancies ( 1,2,3,4 ) . pmec is classified as a salivary gland type lung carcinoma , which originates from the submucosal glands of the trachea and bronchus ( 5,6 ) . histologic grade , cancer stage and lymph node metastasis are reported independent factors for long - term prognosis in patients with pmec ( 5 ) . it is now generally accepted that low - grade pmec behaves like a benign or low - grade malignant tumor , while high - grade pmec shows virulent characteristics like any other non - small cell lung cancer and has occasional lymph node metastasis . therefore , if tumor grade could be predicted before surgery , it might reduce unnecessary lymph node dissection and even preserve lung function with limited pulmonary resection in patients with low - grade pmec . on the other hand , in cases expected to have high - grade tumor , extended pulmonary resection with more radical lymph node dissection or neoadjuvant treatments could be performed . however , there is no diagnostic tool to predict tumor grade prior to surgery for pmec . this study evaluated whether the maximum standardized uptake value ( suvmax ) of fluorine-18 fluorodeoxyglucose positron emission tomography / computed tomography ( f - fdg pet / ct ) is a significant predictor for pathologic grade and postsurgical outcomes in patients following surgery for pmec . this retrospective study was approved by our hospital 's institutional review board . from 2005 to 2013 , 27 patients ( 0.5% of all primary lung cancer patients ) underwent complete resection with curative intent for pmec . four patients with pet / cts taken at other hospitals or without studies prior to surgery were excluded from enrollment . patients were instructed to fast for six hours prior to receiving 370 mbq ( 10 mci ) of f - fdg by intravenous injection . forty - five minutes after the injection , pet / ct scans ( ge healthcare ; milwaukee , wi , usa ) were performed . from 2005 to 2008 , a discovery ls scanner was used for pet / ct in eight patients . ct was performed at 140 kev , 40 - 120 ma , tube rotation time of 0.5 seconds per rotation , pitch of 6 , and section thickness of 5 mm . from 2008 to 2013 , a discovery ste scanner was used for the other 15 patients , with ct performed at 140 kev , 30 - 170 ma , tube rotation time of 0.5 seconds per rotation , pitch of 6 , and section thickness of 3.75 mm . pet data sets were reconstructed iteratively with an ordered subsets expectation - maximization algorithm and a segmented attenuation correction ( two iterations , 28 subsets ) , and also with the ct data . commercial software ( advantage workstation version 4.4 ; ge healthcare ) was used to accurately co - register the separate ct and pet scan data . the suvmax of the primary tumor was measured by the software . in brief , a volume - of - interest encircling the whole primary tumor was manually drawn , taking into account the ct , pet and fused pet / ct images , which allowed the software to automatically show the suvmax of primary tumor . tumors were located in the segmental bronchi or lobar bronchus in 17 patients , main bronchus in five patients and trachea in one patient . complete resection of the tumor ( r0 ) was histologically confirmed in all subjects , and every operation also included mediastinal lymph node dissection . there were nine lobectomies , seven sleeve lobectomies , one bilobectomy , one sleeve bilobectomy , three pneumonectomies , one bronchial wedge resection , and one tracheal resection and anastomosis . eighteen patients underwent pulmonary resection via open thoracotomy , and five patients underwent video - assisted thoracoscopic surgery ( vats ) . the patients visited the outpatient clinic and had ct or pet / ct scans every three months for two years after surgery and then every six months for three more years . patient survival was reviewed , and the end date was defined as the latest follow - up date or the date of patient death . disease - free survival was defined as the time between diagnosis and the first clinical or pathologic evidence of loco - regional or distant recurrent disease . histopathologic tumor grade was defined according to the grading system of the armed forces institute of pathology ( 15,16 ) . tumors that met the criteria for grade 1 were classified as low - grade tumors in our study . similarly , tumors that met the grade 2 and 3 criteria were classified as high - grade tumors . overall , there were 16 patients with low - grade tumors and seven patients with high - grade tumors ( one patient with grade 2 , six patients with grade 3 ) . pathologic staging was classified according to the 7th american joint committee on cancer staging criteria . all data were statistically analyzed using stata statistical software 2007 , version 10 ( statacorp lp , college station , tx , usa ) . suvmax of the main tumor in pet / ct images was correlated with tumor grade . the optimal cutoff value was calculated as 6.5 by receiver operating characteristic ( roc ) curve and area under curve was 0.92 . patients with a suvmax of 6.5 or higher were assigned to the high suv group ( n = 7 ) and the rest were assigned to the low suv group ( n = 16 ) . we compared tumor grade , pathologic stage , and long - term outcomes between the low suv group and the high suv group . tests were performed for categorical variables , and unpaired t tests were performed for continuous variables . overall survival was analyzed with kaplan - meier curves and the log - rank test . this retrospective study was approved by our hospital 's institutional review board . from 2005 to 2013 , 27 patients ( 0.5% of all primary lung cancer patients ) underwent complete resection with curative intent for pmec . four patients with pet / cts taken at other hospitals or without studies prior to surgery were excluded from enrollment . patients were instructed to fast for six hours prior to receiving 370 mbq ( 10 mci ) of f - fdg by intravenous injection . forty - five minutes after the injection , pet / ct scans ( ge healthcare ; milwaukee , wi , usa ) were performed . from 2005 to 2008 , a discovery ls scanner was used for pet / ct in eight patients . ct was performed at 140 kev , 40 - 120 ma , tube rotation time of 0.5 seconds per rotation , pitch of 6 , and section thickness of 5 mm . from 2008 to 2013 , a discovery ste scanner was used for the other 15 patients , with ct performed at 140 kev , 30 - 170 ma , tube rotation time of 0.5 seconds per rotation , pitch of 6 , and section thickness of 3.75 mm . pet data sets were reconstructed iteratively with an ordered subsets expectation - maximization algorithm and a segmented attenuation correction ( two iterations , 28 subsets ) , and also with the ct data . commercial software ( advantage workstation version 4.4 ; ge healthcare ) was used to accurately co - register the separate ct and pet scan data . the suvmax of the primary tumor was measured by the software . in brief , a volume - of - interest encircling the whole primary tumor was manually drawn , taking into account the ct , pet and fused pet / ct images , which allowed the software to automatically show the suvmax of primary tumor . tumors were located in the segmental bronchi or lobar bronchus in 17 patients , main bronchus in five patients and trachea in one patient . complete resection of the tumor ( r0 ) was histologically confirmed in all subjects , and every operation also included mediastinal lymph node dissection . there were nine lobectomies , seven sleeve lobectomies , one bilobectomy , one sleeve bilobectomy , three pneumonectomies , one bronchial wedge resection , and one tracheal resection and anastomosis . eighteen patients underwent pulmonary resection via open thoracotomy , and five patients underwent video - assisted thoracoscopic surgery ( vats ) . the patients visited the outpatient clinic and had ct or pet / ct scans every three months for two years after surgery and then every six months for three more years . patient survival was reviewed , and the end date was defined as the latest follow - up date or the date of patient death . disease - free survival was defined as the time between diagnosis and the first clinical or pathologic evidence of loco - regional or distant recurrent disease . histopathologic tumor grade was defined according to the grading system of the armed forces institute of pathology ( 15,16 ) . tumors that met the criteria for grade 1 were classified as low - grade tumors in our study . similarly , tumors that met the grade 2 and 3 criteria were classified as high - grade tumors . overall , there were 16 patients with low - grade tumors and seven patients with high - grade tumors ( one patient with grade 2 , six patients with grade 3 ) . pathologic staging was classified according to the 7th american joint committee on cancer staging criteria . all data were statistically analyzed using stata statistical software 2007 , version 10 ( statacorp lp , college station , tx , usa ) . suvmax of the main tumor in pet / ct images was correlated with tumor grade . the optimal cutoff value was calculated as 6.5 by receiver operating characteristic ( roc ) curve and area under curve was 0.92 . patients with a suvmax of 6.5 or higher were assigned to the high suv group ( n = 7 ) and the rest were assigned to the low suv group ( n = 16 ) . we compared tumor grade , pathologic stage , and long - term outcomes between the low suv group and the high suv group . tests were performed for categorical variables , and unpaired t tests were performed for continuous variables . overall survival was analyzed with kaplan - meier curves and the log - rank test . the mean age was significantly higher in the high suv group than the low suv group ( 57.6  11.7 years vs. 39.6  17.2 years respectively , p = 0.010 ) . notably , all three patients under age 20 were included in the low suv group and had a low grade tumor . most of the patients ( 87.0% ) showed an eastern cooperative oncology group performance score of 0 or 1 and only three patients had a performance score of 2 ( two patients from high suv group and one patient from low suv group ) . the mean suvmax was 15.4  11.5 in the high suv group and 3.9  1.3 in the low suv group . 0.001 ) and larger tumor sizes ( 43.6  9.0 mm vs. 21.4  3.0 mm , p = 0.003 ) . typical enhanced ct and pet / ct images of low suv group are presented in figure 2 and images of high suv group in figure 3 . the high suv group also had more frequent t3/4 stage ( 72.4% vs. 6.3% , p = 0.006 ) , more frequent lymph node metastases ( 57.1% vs. 0% , p = 0.001 ) , and consequently , higher cancer stages ( stage i / ii vs. iii , p = 0.001 ) than the low suv group . enhanced ct and pet / ct images of the patient with regional lymph node metastasis are presented in figure 4 . the low suv group had low grade tumors , except for one patient , and no lymph node metastasis . the sensitivity and specificity of pet / ct for predicting tumor grade were 85.7% and 93.8% , respectively . accuracy was 91.3% and the positive and negative predictive value was 85.7% and 93.8% , respectively . length of follow - up was similar between the two groups ( mean 48.6  38.7 months ; p = 0.660 ) . in the high suv group , four patients ( 57.1% ) suffered cancer recurrence during follow - up , and one died of cancer 5 months after surgery . another patient from high suv group showed no evidence of cancer recurrence , but died of brain infarct during the follow - up . in contrast , none of the patients in the low suv group experienced recurrence or mortality . as a result , the 5-year overall survival rate was significantly higher in the low suv group than the high suv group ( 100% vs. 71.4% respectively , p = 0.031 ) . three - year disease - free survival was also significantly higher in the low suv group ( 100% vs. 17.9% respectively , p < 0.001 ) . high grade tumor ( p < 0.001 ) , pathologic stage iii ( p multivariate analysis for long - term survival was unavailable , because there was no mortality or recurrence in patients with the low suv group . kaplan - meier curves of overall and disease - free survival rates according to suv group are diagrammed in figure 5 . since fdg - pet uptake in pmec was first reported in a 5-year - old girl ( 17 ) , several studies have addressed the subject . case of low - grade pmec without nodal metastasis and reported a suvmax of 3.63 ( 18 ) and 6.2 ( 19 ) . a case report involving high - grade pmec with the suvmax data from these studies precisely matches our results , further suggesting that a suvmax higher than 6.5 indicates a possible high - grade tumor . suvmax in salivary gland type carcinoma ( including seven cases of pmec ) reportedly tends to be greater in high - grade tumors ( 21 ) . additionally , a recent study concerning surgical outcomes in 14 patients with pmec , the median suvmax increased significantly along with tumor grade ( p = 0.041 ) ( 14 ) . presently , pet revealed significant differences ( p < 0.001 ) in tumor grade according to suv group . high fdg uptake has been associated with more frequent nodal or distant metastases , but failed to predict long - term survival ( 22 ) . however in this study , pet / ct data was available in 11 patients ( 36.7% ) and other subtypes of salivary gland type lung cancer were included . presently , nodal metastasis was significantly associated with the high suv group ( p = 0.001 ) . furthermore , overall and disease - free survivals were significantly better in the low suv group . to our knowledge , this is the first study to report the prognostic value of fdg - pet / ct for long - term outcomes in pmec patients . the low suv group had good long - term prognosis without recurrence after complete resection of tumor . in contrast , despite complete resection , the high suv group suffered from local or distant recurrence . in the high suv group , these results are similar to the prior conclusion that adjuvant chemotherapy does not seem to be effective in high grade pmec ( 23 ) . the most common site of pmec in the tracheobronchial tree is the segmental bronchi , which are located within the lung parenchyma . in the present study , nine patients ( 56.3% ) in the low suv group underwent simple lobectomies , and five of these simple lobectomies were performed by vats . even in patients who required sleeve resection of the bronchus , vats could be attempted . use of vats sleeve lobectomy in low - grade pmec in the left main bronchus has been described ( 24 ) . therefore , in selected patients with low pet / ct uptake , vats represents a feasible and effective surgical option . considering the rarity of pmec , multi - center studies with large number of cases are needed to reconfirm and support the results of this study . another limitation is that the change in pet / ct device once during follow - up might have caused alteration of suvmax , although the differences were likely minimal . in conclusion , f - fdg pet / ct appears to be a useful preoperative imaging modality for predicting tumor grade , nodal stage and postsurgical prognosis . patients with a suvmax greater than 6.5 were more likely to have a high - grade tumor , lymph node metastasis and cancer recurrence . therefore , pmec patients with high uptake on pet / ct imaging might require aggressive mediastinal lymph node dissection and adjuvant therapies . further studies with more cases of pmec are necessary to verify the validity of pet / ct for prediction of long - term prognosis .
objectivethe maximum standardized uptake value ( suvmax ) of pulmonary mucoepidermoid carcinoma ( pmec ) in fluorine-18fluorodeoxyglucose positron emission tomography / computed tomography ( 18f - fdg pet / ct ) was evaluated as a preoperative predictor of pathologic grade and survival rate.materials and methodstwenty - three patients who underwent preoperative pet / ct and complete resection for pmec were enrolled . 
 the optimal cut - off suvmax for tumor grade was calculated as 6.5 by receiver operating characteristic curve . 
 the patients were divided into a high suv group ( n = 7 ) and a low suv group ( n = 16 ) . 
 clinicopathologic features were compared between the groups by 2 test and overall survival was determined by kaplan - meier analysis.resultsthe mean suvmax was 15.4  11.5 in the high suv group and 3.9  1.3 in the low suv group . 
 all patients except one from the low suv group had low grade tumors and all had no nodal metastasis . the sensitivity and specificity of suvmax from pet / ct for predicting tumor grade was 85.7% and 93.8% , respectively . during the follow - up period ( mean , 48.6  38.7 months ) , four patients from the high suv group experienced cancer recurrence , and one died of cancer . in contrast , none of the low suv group had recurrence or mortality . 
 five - year overall survival rate was significantly higher in the low suv group ( 100% vs. 71.4% , p = 0.031).conclusionpulmonary mucoepidermoid carcinoma patients with high suvmax in pet / ct had higher tumor grade , more frequent lymph node metastasis and worse long - term outcome . 
 therefore , pmec patients with high uptake on pet / ct imaging might require aggressive mediastinal lymph node dissection and adjuvant therapies .