the online version of this article ( doi:10.1007/s00259 - 012 - 2182 - 0 ) contains supplementary material , which is available to authorized users . melanoma is a tumour with one of the most rapidly increasing incidence rates , especially in caucasian populations . in a decade , its incidence in the netherlands has risen by 63  % to 21.7/100,000 ( european standardized rate ) from 13.3/100,000 in 1998 . standard treatment for patients with palpable lymph node metastases ( ajcc stage iiib ) is therapeutic lymph node dissection ( tlnd ) . . established prognostic factors in patients with stage iiib melanoma are the number and size of metastatic nodes , and the presence of extranodal growth [ 2 , 3 ] . identification of additional prognostic factors could lead to more individualized treatment and follow - up schemes . whole - body f - fdg pet is a sensitive screening tool in patients with high - risk melanoma , since melanomas are typically fdg - avid . the added value of fdg pet over ct with respect to diagnostic accuracy and impact on management has been established in several studies [ 410 ] . besides improved detection of metastases , a standard clinical pet / ct scan offers the opportunity to quantify the level of glucose metabolism in tumours . glucose metabolism , as assessed with fdg , is an epiphenomenon of cancer and seems to have prognostic value [ 1117 ] . however , the value of fdg as a prognostic biomarker is not undisputed , probably as a consequence of confounding and heterogeneity in both the clinical spectrum and pet technology . we have reported some preliminary data acquired in a retrospective setting suggesting an inverse relationship between tumour fdg uptake in patients with stage iii melanoma who receive surgery with curative intent . the present study aimed to prospectively validate these findings taking into account the above - mentioned potential confounders . from november 2003 until march 2008 , all patients with palpable , histology- or cytology - proven lymph node metastases of melanoma referred to the university medical centre groningen ( umcg ) for fdg pet and ct examination were prospectively included in this study . prior to study entry , all patients were considered candidates for tlnd , and they took part in a large prospective multicentre study to assess the diagnostic performance of fdg pet and multislice ct . inclusion criteria for the present study were : stage iii after fdg pet and abdominal / thoracic ct , candidate for tlnd with curative intent , and scanned on the same fdg pet scanner with identical patient preparation , acquisition and reconstruction protocols . follow - up was uniform in all patients and consisted of clinical evaluation of physical signs and symptoms at standard follow - up visits ( every 3  months in the first year , every 4  months in the second year , twice a year in the third to fifth years , and every year in the sixth to tenth years ) ; diagnostic tests ( chest radiography , ct or fdg pet ) were only indicated if distant metastases were suspected . fdg was synthesized on - site according to the method described by hamacher et al . using an automated synthesis module . prior to fdg pet imaging , patients were instructed to fast for at least 6  h and to drink 1  l of water . after intravenous injection of fdg , whole - body imaging was performed in the two - dimensional mode using a siemens ecat exact hr+ scanner ( siemens / cti , knoxville , tn ) , applying emission scans of 5  min per bed position , starting 90  min after the injection of fdg . image reconstructions were iterative ( ordered subset expectation maximization ) with eight subsets and two iterations . all scans were corrected for decay , scatter , randoms and attenuation , and normalized . the postreconstruction filter ( gaussian postprocessing filter ) was 5  mm , yielding an estimated spatial resolution ( full - width at half - maximum ) of 7  mm . fdg uptake was calculated as suv ( radioactivity concentration in tissue in becquerels per cubic centimetre / injected dose in becquerels / patient body weight in grams ) . three - dimensional volumes of interest were placed semiautomatically around the lymph node metastasis with the highest fdg uptake ( visual assessment ) using dedicated software ( idl - viewer , leuven ) . the numerator of the suv was chosen to measure either the mean counts within an isocontour to 70  % of the voxels with the highest counts , or the maximum itself , yielding suvmean or suvmax , respectively . to explore the distribution of suvmean and suvmax a kernel density plot was used , which approximates the probability density of the variable ; kernel density plots have the advantage of being independent of the choice of origin , unlike histograms . the associations between suvmean / suvmax or the log - transformation ( which gave the best fit ) and patient characteristics were assessed using student s t - test or analysis of variance . patients were divided into two groups ( high and low suv ) based on the median value of the log(suvmean ) and log(suvmax ) for the survival analysis . this dichotomization led to the same patient categorization for suvmax and suvmean in 95  % of the patients . since repeatability of suvmean is superior to that of suvmax [ 20 , 21 ] , we show the suvmean results in the analyses . survival was analysed in terms of disease - free survival ( dfs ) and disease - specific survival ( dss ) . an event was recorded for any recurrence ; for dss an event was recorded if the patient died due to melanoma metastases . multivariable models were created with age , gender , location of the lymph nodes defined as cervical region , axilla or groin , number of nodes removed during tlnd , number of lymph nodes positive on histopathology after tlnd , tumour size in the largest lymph node metastasis determined after tlnd by histopathology , extranodal growth defined as metastatic tumour which clearly extended ( histologically ) through the nodal capsule into the perinodal fatty tissue or tumour involvement in the hilar region with interruption of the smooth outline of the ( presumed ) capsule , breslow thickness and ulceration of the primary melanoma , and high or low suvmean . from november 2003 until march 2008 , all patients with palpable , histology- or cytology - proven lymph node metastases of melanoma referred to the university medical centre groningen ( umcg ) for fdg pet and ct examination were prospectively included in this study . prior to study entry , all patients were considered candidates for tlnd , and they took part in a large prospective multicentre study to assess the diagnostic performance of fdg pet and multislice ct . inclusion criteria for the present study were : stage iii after fdg pet and abdominal / thoracic ct , candidate for tlnd with curative intent , and scanned on the same fdg pet scanner with identical patient preparation , acquisition and reconstruction protocols . follow - up was uniform in all patients and consisted of clinical evaluation of physical signs and symptoms at standard follow - up visits ( every 3  months in the first year , every 4  months in the second year , twice a year in the third to fifth years , and every year in the sixth to tenth years ) ; diagnostic tests ( chest radiography , ct or fdg pet ) were only indicated if distant metastases were suspected . fdg was synthesized on - site according to the method described by hamacher et al . using an automated synthesis module . prior to fdg pet imaging , patients were instructed to fast for at least 6  h and to drink 1  l of water . after intravenous injection of fdg , whole - body imaging was performed in the two - dimensional mode using a siemens ecat exact hr+ scanner ( siemens / cti , knoxville , tn ) , applying emission scans of 5  min per bed position , starting 90  min after the injection of fdg . image reconstructions were iterative ( ordered subset expectation maximization ) with eight subsets and two iterations . all scans were corrected for decay , scatter , randoms and attenuation , and normalized . the postreconstruction filter ( gaussian postprocessing filter ) was 5  mm , yielding an estimated spatial resolution ( full - width at half - maximum ) of 7  mm . fdg uptake was calculated as suv ( radioactivity concentration in tissue in becquerels per cubic centimetre / injected dose in becquerels / patient body weight in grams ) . three - dimensional volumes of interest were placed semiautomatically around the lymph node metastasis with the highest fdg uptake ( visual assessment ) using dedicated software ( idl - viewer , leuven ) . the numerator of the suv was chosen to measure either the mean counts within an isocontour to 70  % of the voxels with the highest counts , or the maximum itself , yielding suvmean or suvmax , respectively . to explore the distribution of suvmean and suvmax a kernel density plot was used , which approximates the probability density of the variable ; kernel density plots have the advantage of being independent of the choice of origin , unlike histograms . the associations between suvmean / suvmax or the log - transformation ( which gave the best fit ) and patient characteristics were assessed using student s t - test or analysis of variance . patients were divided into two groups ( high and low suv ) based on the median value of the log(suvmean ) and log(suvmax ) for the survival analysis . this dichotomization led to the same patient categorization for suvmax and suvmean in 95  % of the patients . since repeatability of suvmean is superior to that of suvmax [ 20 , 21 ] , we show the suvmean results in the analyses . survival was analysed in terms of disease - free survival ( dfs ) and disease - specific survival ( dss ) . an event was recorded for any recurrence ; for dss an event was recorded if the patient died due to melanoma metastases . multivariable models were created with age , gender , location of the lymph nodes defined as cervical region , axilla or groin , number of nodes removed during tlnd , number of lymph nodes positive on histopathology after tlnd , tumour size in the largest lymph node metastasis determined after tlnd by histopathology , extranodal growth defined as metastatic tumour which clearly extended ( histologically ) through the nodal capsule into the perinodal fatty tissue or tumour involvement in the hilar region with interruption of the smooth outline of the ( presumed ) capsule , breslow thickness and ulceration of the primary melanoma , and high or low suvmean . there were slightly more women : 41 women ( 51.2  % ) , 39 men ( 48.8  % ) . lymph node metastases were located in the groin ( 55.0  % ) , axilla ( 32.5  % ) or cervical region ( 12.5  % ) . the median number of removed nodes was 16 ( range 748 ) and the median number of positive nodes was 2 ( range 119 ) . the tumour size in the lymph node ranged from 0.5 to 7.0  cm with a median of 3.1  cm . in 25 patients ( 31.2  % ) extranodal growth was recorded.table 1patient and tumour characteristics of the 80 patients with palpable , histology- or cytology - proven lymph node metastases of melanomacharacteristicvaluegender , n ( % ) men39 ( 48.8)women41 ( 51.2)age ( years ) , n ( % ) < 50  25 ( 31.2)506532 ( 40.0)>6523 ( 28.8)primary melanomalocation , n ( % ) upper extremities9 ( 11.2)lower extremities34 ( 42.5)trunk29 ( 36.3)head and neck6 ( 7.5)unknown primary2 ( 2.5)breslow thickness ( mm ) , n ( % ) 1.010 ( 12.5)1.02.027 ( 33.8)2.041 ( 51.2)unknown primary2 ( 2.5)ulceration , n ( % ) no63 ( 78.8)yes15 ( 18.7)unknown primary2 ( 2.5)lymph node metastaseslocation , n ( % ) cervical region10 ( 12.5)axilla26 ( 32.5)groin44 ( 55.0)removed nodes , median ( range)16 ( 748)positive nodes , median ( range)2 ( 119)tumour size , median ( range)3.1 ( 0.57.0)extranodal growth , n ( % ) no55 ( 68.8)yes25 ( 31.2 ) patient and tumour characteristics of the 80 patients with palpable , histology- or cytology - proven lymph node metastases of melanoma as shown in fig .  1 , the suv values were not normally distributed ( no gaussian distribution ) . a log - transformation of the suvmean and suvmax values provided the best fit to a gaussian distribution . the log - transformed suvmean and suvmax values were not associated with gender ( p  =  0.3 and p  =  0.4 ) , age ( p  =  0.2 and p  =  0.1 ) , location of the lymph nodes ( p  =  0.2 for both ) , number of removed nodes ( p  =  0.4 for both ) , number of positive nodes ( p  =  0.1 for both ) or extranodal growth ( p  =  0.6 for both ) , respectively . suv was , however , associated with size of the melanoma metastasis in the lymph node ( p  <  0.001).fig . 1distributions of the suvmean and suvmax values in comparison with the normal ( gaussian ) distributions distributions of the suvmean and suvmax values in comparison with the normal ( gaussian ) distributions during the follow - up ( median 3.0  years , range : 0.38.2  years , in all patients ; 5.5  years , 3.18.2 years , in patients without an event ) , 55 patients ( 68.8  % ) developed a recurrence . overall , 49 patients ( 61.3  % ) died as a result of the recurrent disease and 6 patients with recurrence were still alive at the end of the study . the median suvmean ( used for further analysis ) was 6.49 ( iqr 4.510.9 ) and the median log(suvmean ) was 1.86 . the 5-year dfs in patients with a low suvmean was 40.9  % ( 95% ci 25.555.7  % ) and 24.2  % ( 95%ci 12.438.0  % ) in patients with a high suvmean ( p  =  0.02 ) , as shown in fig .  2 . webtable 1 shows the univariate and multivariable analysis of dfs , and table  2 shows the analysis of dfs in relation to suv . suvmean was associated with dfs with a hazard ratio ( hr ) of 1.7 ( 95% ci 1.03.0 ; p  =  0.048 ) . other variables associated with dfs in the multivariable analysis were the number of positive nodes ( hr 1.1 , 95% ci 1.01.2 ; p  =  0.02 ) and the presence of extranodal growth ( hr 3.4 , 95% ci 1.44.2 ; p  =  0.003).fig . 2kaplan meier curves for dfs and dss in patients with a high and low suvtable 2multivariable analyses of dfs and dss for the patients with stage iii melanomavariabledfsdsshazard ratiop valuehazard ratiop valuesuvlow1 ( reference)0.0481 ( reference)0.1high1.74 ( 1.003.00)1.57 ( 0.862.87)adjusted for positive nodes and extranodal growth ( see webtable).adjusted for sex , positive nodes and extranodal growth ( see webtable).divided by the median of log(suvmean )  =  1.86 . kaplan meier curves for dfs and dss in patients with a high and low suv multivariable analyses of dfs and dss for the patients with stage iii melanoma adjusted for positive nodes and extranodal growth ( see webtable ) . adjusted for sex , positive nodes and extranodal growth ( see webtable ) . the 5-year dss was 47.5  % ( 95% ci 30.962.3 ) in patients with a low suvmean and 30.3  % ( 95% ci 16.745.0 ) for patients with a high suvmean ( p  =  0.02 , fig .  2 ) . webtable 2 shows the univariate and multivariable analysis of dss , and table  2 shows the analysis of dss in relation to suv . suvmean was not associated with dss in the multivariable analysis ( hr 1.6 , 95% ci 0.92.9 ; p  =  0.1 ) . female gender was associated with a better dss in the multivariable analysis ( hr 0.5 , 95% ci 0.30.8 ; p  =  0.009 ) . during the follow - up ( median 3.0  years , range : 0.38.2  years , in all patients ; 5.5  years , 3.18.2 years , in patients without an event ) , 55 patients ( 68.8  % ) developed a recurrence . overall , 49 patients ( 61.3  % ) died as a result of the recurrent disease and 6 patients with recurrence were still alive at the end of the study . the median suvmean ( used for further analysis ) was 6.49 ( iqr 4.510.9 ) and the median log(suvmean ) was 1.86 . the 5-year dfs in patients with a low suvmean was 40.9  % ( 95% ci 25.555.7  % ) and 24.2  % ( 95%ci 12.438.0  % ) in patients with a high suvmean ( p  =  0.02 ) , as shown in fig .  2 . webtable 1 shows the univariate and multivariable analysis of dfs , and table  2 shows the analysis of dfs in relation to suv . suvmean was associated with dfs with a hazard ratio ( hr ) of 1.7 ( 95% ci 1.03.0 ; p  =  0.048 ) . other variables associated with dfs in the multivariable analysis were the number of positive nodes ( hr 1.1 , 95% ci 1.01.2 ; p  =  0.02 ) and the presence of extranodal growth ( hr 3.4 , 95% ci 1.44.2 ; p  =  0.003).fig . 2kaplan meier curves for dfs and dss in patients with a high and low suvtable 2multivariable analyses of dfs and dss for the patients with stage iii melanomavariabledfsdsshazard ratiop valuehazard ratiop valuesuvlow1 ( reference)0.0481 ( reference)0.1high1.74 ( 1.003.00)1.57 ( 0.862.87)adjusted for positive nodes and extranodal growth ( see webtable).adjusted for sex , positive nodes and extranodal growth ( see webtable).divided by the median of log(suvmean )  =  1.86 . kaplan meier curves for dfs and dss in patients with a high and low suv multivariable analyses of dfs and dss for the patients with stage iii melanoma adjusted for positive nodes and extranodal growth ( see webtable ) . adjusted for sex , positive nodes and extranodal growth ( see webtable ) . the 5-year dss was 47.5  % ( 95% ci 30.962.3 ) in patients with a low suvmean and 30.3  % ( 95% ci 16.745.0 ) for patients with a high suvmean ( p  =  0.02 , fig .  2 ) . webtable 2 shows the univariate and multivariable analysis of dss , and table  2 shows the analysis of dss in relation to suv . suvmean was not associated with dss in the multivariable analysis ( hr 1.6 , 95% ci 0.92.9 ; p  =  0.1 ) . female gender was associated with a better dss in the multivariable analysis ( hr 0.5 , 95% ci 0.30.8 ; p  =  0.009 ) . the present prospective study endorses the prognostic value of suv in terms of dfs in patients with stage iiib melanoma who have been optimally staged with fdg pet and ct . the use of suv as a quantitative parameter of fdg uptake has a long tradition in nuclear medicine . although its value for predicting tumour response to therapy has become generally accepted , the clinical usefulness and applicability of suv for prognostic purposes is still under discussion . as far as the authors are aware there are two other studies ( from our group ) that addressed the value of suv in melanoma patients [ 13 , 22 ] . the first study was a small retrospective study that showed no significant association between suvmean and survival ( p  =  0.11 ) ; however , dfs was significantly decreased in patients with a high suvmean ( p  =  0.03 ) . there are , however , significant differences between the patients in the two databases , especially in location , number of positive nodes ( more in the present study ) and percentage of patients with extranodal growth ( lower percentage in the present study ) . furthermore , the cut - off values in both studies were data - driven and differ . in the present prospective study we confirmed the association found in the retrospective study . there was a significantly decreased dfs in patients with a high suvmean in the lymph node metastasis ( p  =  0.048 ) . dss was , however , associated with gender , as reported previously by de vries et al . . among 10,538 melanoma patients , women had a superior survival than men even after adjustment for multiple confounding variables . probably factors other than stage at diagnosis and location reduces mortality risk in female melanoma patients . the associations between extranodal growth and the number of nodes have been reported before : extranodal growth showed a stronger association with dfs than suvmean . some of the primary melanoma characteristics such as breslow thickness and ulceration were not associated with survival in these patients with macrometastatic disease . interestingly , a recent study by balch et al . showed similar results : in patients with nodal micrometastases , multiple covariates independently predicted survival , including several primary melanoma features ( thickness , mitotic rate , ulceration , and anatomic site of the primary tumour ) . in contrast , in patients with nodal macrometastases , primary melanoma characteristics did not predict survival . remarkably , there was no clear significant association between tumour size and survival in the present study . categorization of tumour size into <3  cm or 3  cm did not lead to different results ( dfs hr 1.7 , 95% ci 1.03.0 ) , p  =  0.1 ; dss unfortunately , we were not able to stratify according to tumour size . further , larger studies should possibly involve stratification according to smaller and larger tumour in the lymph nodes . we present a single - centre study with standardized pet procedures to obtain homogeneity at that level . since the measured suv is a function of many technical and biological factors , the absolute values are only generalizable if these are taken into account . a recent study by westerterp et al . showed differences in suv quantification between institutes with different pet scanners . consequently , standardization of acquisition , reconstruction and data analysis is needed for multicentre trials . when the present study was initiated , there were no guidelines on how to harmonize the results of multicentre studies using different scanners , acquisition and reconstruction protocols . however , provided that the 2010 pet guidelines for trials and clinical practice are followed , this is no longer an obstacle , and hopefully the evidence for the potential of quantitative pet in oncology will mature rapidly . in the present study we used the median value of the log - transformed suvmean for risk stratification . however , there is always change for bias if data - driven cut - off values are used . to be a practical prognostic factor in routine practice , standardization of protocols and cut - off values for suv should be agreed upon or the methodology to determine the optimal threshold for each centre should be established . as a fdg pet scan as a staging procedure prior to treatment of metastatic melanoma in regional lymph nodes is now performed , determination of suv values would provide additional information at very little extra cost . in conclusion , in patients with clinical stage iii melanoma , a high suvmean was associated with decreased dfs . if confirmed in larger studies , suvmean could potentially be used , in addition to the number of positive nodes , tumour size and extranodal growth , as a factor in deciding on adjuvant systemic treatment . this article is distributed under the terms of the creative commons attribution license which permits any use , distribution , and reproduction in any medium , provided the original author(s ) and the source are credited .
purposefdg pet / ct is an excellent tool to detect melanoma metastases and also allows quantification of fdg uptake using standardized uptake value ( suv ) . 
 the aim of this study was to prospectively investigate the potential prognostic value of suv for disease - free survival ( dfs ) and disease - specific survival ( dss ) for patients with stage iiib melanoma.methodsfrom november 2003 to march 2008 , all consecutive patients were included in the present study . 
 inclusion criteria were : palpable , histology- or cytology - proven lymph node metastases of melanoma , and referred to the university medical centre groningen for fdg pet and ct examination . 
 patients without distant metastases were evaluated . 
 multivariable survival analysis was performed to determine whether suv was associated with dfs and dss ( cox proportional hazard analysis).resultsin 80 patients ( without distant metastases , 65  % ) suv could be measured . 
 overall 5-year dfs was 41  % ( 95% ci 2656  % ) and 24  % ( 95% ci 1238  % ) in patients with a low and high suvmean ( p  =  0.02 ) , respectively . 
 overall 5-year dss was 48  % ( 95% ci 3162  % ) and 30  % ( 95% ci 1745  % ) in patients with a low and high suvmean ( p  =  0.04 ) , respectively . in the multivariable analysis , 
 suvmean was associated with dfs ( hazard ratio 1.7 ; p  =  0.048 ) , but was not associated with dss ( hazard ratio 1.6 ; p  =  0.1 ) . the number of positive nodes , extranodal growth and gender were also associated with survival.conclusionfdg uptake in clinically overt nodal melanoma metastases is inversely associated with dfs . 
 univariate analysis showed an association with dss . 
 however , after adjustment for potential confounders this association was no longer significant . if these findings are confirmed in larger studies , suvmean could potentially be used ( in addition to the number of positive nodes , tumour size and extranodal growth ) as a factor in deciding on adjuvant systemic treatment.electronic supplementary materialthe online version of this article ( doi:10.1007/s00259 - 012 - 2182 - 0 ) contains supplementary material , which is available to authorized users .