Invited Commentary

Abstract

Although the [F-18]fluorodeoxyglucose (FDG) uptake on positron emission tomography (PET) had already been associated with tumor aggressiveness in lung tumors [1Vesselle H. Schmidt R.A. Pugsley J.M. et al.Lung cancer proliferation correlates with [F-18]fluorodeoxyglucose uptake by positron emission tomography.Clin Cancer Res. 2000; 6: 3837-3844PubMed Google Scholar, 2Nomori H. Watanabe K. Ohtsuka T. et al.Fluorine 18-tagged fluorodeoxyglucose positron emission tomographic scanning to predict lymph node metastasis, invasiveness, or both, in clinical T1 N0 M0 lung adenocarcinoma.J Thorac Cardiovasc Surg. 2004; 128: 396-401Abstract Full Text Full Text PDF PubMed Scopus (43) Google Scholar], only a few clinical studies have been conducted about the usefulness of FDG-PET scans for the evaluation of thymic epithelial tumor aggressiveness [3Liu Y. Characterization of thymic lesions with F-18 FDG PET-CT: an emphasis on epithelial tumors.Nucl Med Commun. 2011; 32: 554-562Crossref PubMed Scopus (16) Google Scholar, 4Sung Y.M. Lee K.S. Kim B.T. Choi J.Y. Shim Y.M. Yi C.A. 18F-FDG PET/CT of thymic epithelial tumors: usefulness for distinguishing and staging tumor subgroups.J Nucl Med. 2006; 47: 1628-1634PubMed Google Scholar]. Some investigators have recently reported that FDG uptake in thymic epithelial tumors was connected with the grade of malignancy and poor outcome, suggesting a promising role of F-18 FDG PET-computed tomography (CT) in the characterization of these lesions [3Liu Y. Characterization of thymic lesions with F-18 FDG PET-CT: an emphasis on epithelial tumors.Nucl Med Commun. 2011; 32: 554-562Crossref PubMed Scopus (16) Google Scholar, 4Sung Y.M. Lee K.S. Kim B.T. Choi J.Y. Shim Y.M. Yi C.A. 18F-FDG PET/CT of thymic epithelial tumors: usefulness for distinguishing and staging tumor subgroups.J Nucl Med. 2006; 47: 1628-1634PubMed Google Scholar]. By contrast, other studies have shown controversial data about the ability of F-18 FDG PET-CT to differentiate invasive (high-risk) and noninvasive (low-risk) thymomas, probably because of a marked overlap in the FDG uptake [5Sasaki M. Kuwabara Y. Ichiya Y. et al.Differential diagnosis of thymic tumors using a combination of 11C-methionine PET and FDG PET.J Nucl Med. 1999; 40: 1595-1601PubMed Google Scholar, 6Travaini L.L. Petralia G. Trifiro G. et al.F18-FDG positron emission tomography/computed tomography and multidetector computed tomography roles in thymic lesion treatment planning.Lung Cancer. 2008; 61: 362-368Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar].Confirming these data, Matsumoto and colleagues [7Matsumoto I. Oda M. Takizawa M. et al.Usefulness of fluorine-18 fluorodeoxyglucose-positron emission tomography in management strategy for thymic epithelial tumors.Ann Thorac Surg. 2013; 95: 305-311Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar] have demonstrated in this article the impossibility of specifying Masaoka stages or the World Health Organization (WHO) histologic subtype with the absolute value of SUVmax, even if advanced Masaoka stages and WHO malignant grade subtypes had high SUVmax. According to the other results of the study, FDG-PET SUVmax also tended to be higher for large tumors (p = .02), and particularly high for Ki-67 positive samples (p = 0004), indicating a strong correlation between SUVmax and Ki-67 LI (p = 0.0001).The interrelation of Ki-67 with both the histologic features and the invasiveness 6of thymoma [4Sung Y.M. Lee K.S. Kim B.T. Choi J.Y. Shim Y.M. Yi C.A. 18F-FDG PET/CT of thymic epithelial tumors: usefulness for distinguishing and staging tumor subgroups.J Nucl Med. 2006; 47: 1628-1634PubMed Google Scholar, 5Sasaki M. Kuwabara Y. Ichiya Y. et al.Differential diagnosis of thymic tumors using a combination of 11C-methionine PET and FDG PET.J Nucl Med. 1999; 40: 1595-1601PubMed Google Scholar] had already been reported in a few other studies, but this study showed for the first time in the literature the correlation between SUVmax and Ki-67 label index (LI), providing a good index for diagnosis and treatment. SUVmax accurately reflected therapeutic efficacy in the induction treatment (IT) cases, with increased treatment efficacy on pathologic evaluation associated with larger decreases in mean SUVmax, showcasing FDG-PET also as a sensitive and specific tool in diagnosing residual disease.One main concern in the use of PET as an instrument for diagnosis and follow-up in thymic epithelial tumors is that FDG uptake could overlap in different grades of invasiveness and is usually proportional to the size of the tumor, although small tumors are not all necessary noninvasive [5Sasaki M. Kuwabara Y. Ichiya Y. et al.Differential diagnosis of thymic tumors using a combination of 11C-methionine PET and FDG PET.J Nucl Med. 1999; 40: 1595-1601PubMed Google Scholar, 6Travaini L.L. Petralia G. Trifiro G. et al.F18-FDG positron emission tomography/computed tomography and multidetector computed tomography roles in thymic lesion treatment planning.Lung Cancer. 2008; 61: 362-368Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar].Thus, SUVmax could be used as a valid index for restaging patients after IT, considering the good relation with Ki-67 LI and tumor aggressiveness, but there are still many concerns regarding the use of SUVmax as a preoperative tool for differentiating thymic tumors. However, further larger prospective studies are required to substantiate these preliminary findings. Although the [F-18]fluorodeoxyglucose (FDG) uptake on positron emission tomography (PET) had already been associated with tumor aggressiveness in lung tumors [1Vesselle H. Schmidt R.A. Pugsley J.M. et al.Lung cancer proliferation correlates with [F-18]fluorodeoxyglucose uptake by positron emission tomography.Clin Cancer Res. 2000; 6: 3837-3844PubMed Google Scholar, 2Nomori H. Watanabe K. Ohtsuka T. et al.Fluorine 18-tagged fluorodeoxyglucose positron emission tomographic scanning to predict lymph node metastasis, invasiveness, or both, in clinical T1 N0 M0 lung adenocarcinoma.J Thorac Cardiovasc Surg. 2004; 128: 396-401Abstract Full Text Full Text PDF PubMed Scopus (43) Google Scholar], only a few clinical studies have been conducted about the usefulness of FDG-PET scans for the evaluation of thymic epithelial tumor aggressiveness [3Liu Y. Characterization of thymic lesions with F-18 FDG PET-CT: an emphasis on epithelial tumors.Nucl Med Commun. 2011; 32: 554-562Crossref PubMed Scopus (16) Google Scholar, 4Sung Y.M. Lee K.S. Kim B.T. Choi J.Y. Shim Y.M. Yi C.A. 18F-FDG PET/CT of thymic epithelial tumors: usefulness for distinguishing and staging tumor subgroups.J Nucl Med. 2006; 47: 1628-1634PubMed Google Scholar]. Some investigators have recently reported that FDG uptake in thymic epithelial tumors was connected with the grade of malignancy and poor outcome, suggesting a promising role of F-18 FDG PET-computed tomography (CT) in the characterization of these lesions [3Liu Y. Characterization of thymic lesions with F-18 FDG PET-CT: an emphasis on epithelial tumors.Nucl Med Commun. 2011; 32: 554-562Crossref PubMed Scopus (16) Google Scholar, 4Sung Y.M. Lee K.S. Kim B.T. Choi J.Y. Shim Y.M. Yi C.A. 18F-FDG PET/CT of thymic epithelial tumors: usefulness for distinguishing and staging tumor subgroups.J Nucl Med. 2006; 47: 1628-1634PubMed Google Scholar]. By contrast, other studies have shown controversial data about the ability of F-18 FDG PET-CT to differentiate invasive (high-risk) and noninvasive (low-risk) thymomas, probably because of a marked overlap in the FDG uptake [5Sasaki M. Kuwabara Y. Ichiya Y. et al.Differential diagnosis of thymic tumors using a combination of 11C-methionine PET and FDG PET.J Nucl Med. 1999; 40: 1595-1601PubMed Google Scholar, 6Travaini L.L. Petralia G. Trifiro G. et al.F18-FDG positron emission tomography/computed tomography and multidetector computed tomography roles in thymic lesion treatment planning.Lung Cancer. 2008; 61: 362-368Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar]. Confirming these data, Matsumoto and colleagues [7Matsumoto I. Oda M. Takizawa M. et al.Usefulness of fluorine-18 fluorodeoxyglucose-positron emission tomography in management strategy for thymic epithelial tumors.Ann Thorac Surg. 2013; 95: 305-311Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar] have demonstrated in this article the impossibility of specifying Masaoka stages or the World Health Organization (WHO) histologic subtype with the absolute value of SUVmax, even if advanced Masaoka stages and WHO malignant grade subtypes had high SUVmax. According to the other results of the study, FDG-PET SUVmax also tended to be higher for large tumors (p = .02), and particularly high for Ki-67 positive samples (p = 0004), indicating a strong correlation between SUVmax and Ki-67 LI (p = 0.0001). The interrelation of Ki-67 with both the histologic features and the invasiveness 6of thymoma [4Sung Y.M. Lee K.S. Kim B.T. Choi J.Y. Shim Y.M. Yi C.A. 18F-FDG PET/CT of thymic epithelial tumors: usefulness for distinguishing and staging tumor subgroups.J Nucl Med. 2006; 47: 1628-1634PubMed Google Scholar, 5Sasaki M. Kuwabara Y. Ichiya Y. et al.Differential diagnosis of thymic tumors using a combination of 11C-methionine PET and FDG PET.J Nucl Med. 1999; 40: 1595-1601PubMed Google Scholar] had already been reported in a few other studies, but this study showed for the first time in the literature the correlation between SUVmax and Ki-67 label index (LI), providing a good index for diagnosis and treatment. SUVmax accurately reflected therapeutic efficacy in the induction treatment (IT) cases, with increased treatment efficacy on pathologic evaluation associated with larger decreases in mean SUVmax, showcasing FDG-PET also as a sensitive and specific tool in diagnosing residual disease. One main concern in the use of PET as an instrument for diagnosis and follow-up in thymic epithelial tumors is that FDG uptake could overlap in different grades of invasiveness and is usually proportional to the size of the tumor, although small tumors are not all necessary noninvasive [5Sasaki M. Kuwabara Y. Ichiya Y. et al.Differential diagnosis of thymic tumors using a combination of 11C-methionine PET and FDG PET.J Nucl Med. 1999; 40: 1595-1601PubMed Google Scholar, 6Travaini L.L. Petralia G. Trifiro G. et al.F18-FDG positron emission tomography/computed tomography and multidetector computed tomography roles in thymic lesion treatment planning.Lung Cancer. 2008; 61: 362-368Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar]. Thus, SUVmax could be used as a valid index for restaging patients after IT, considering the good relation with Ki-67 LI and tumor aggressiveness, but there are still many concerns regarding the use of SUVmax as a preoperative tool for differentiating thymic tumors. However, further larger prospective studies are required to substantiate these preliminary findings. Usefulness of Fluorine-18 Fluorodeoxyglucose-Positron Emission Tomography in Management Strategy for Thymic Epithelial TumorsThe Annals of Thoracic SurgeryVol. 95Issue 1PreviewThis study investigated the usefulness of fluorine-18 fluorodeoxyglucose-positron emission tomography (FDG-PET) during the treatment of thymic epithelial tumors in combination with Ki-67 evaluation based on surgical cases in our department. Full-Text PDF