Reply to Bertolaccini et al.

Abstract

We thank Bertolaccini et al. [1] for their interest in our paper [2] and appreciate the opportunity to reply. To begin with, we would like to point out some misunderstandings with regard to our paper. In our analysis, we divided 58 patients with thymic epithelial tumours into three groups according to a simplified histological classification: low-risk thymomas (Types A, AB and B1, n = 23), high-risk thymomas (Types B2 and B3, n = 21) and thymic carcinomas (n = 14). The maximum standardized uptake value (SUVmax) of the thymic carcinomas was significantly higher than those of the low-risk and high-risk thymomas (P < 0.001, respectively). No significant differences were observed between the low-risk thymomas and the high-risk thymomas (P = 0.204). In addition, as shown in Figure 3 in our article, the SUVmax of the Stages III and IV thymomas showed a higher trend towards Stages I and II thymomas (P = 0.060). We excluded thymic carcinoma cases in this analysis because the majority of them were in advanced stages. Although no significant differences were observed between the low-risk and the high-risk thymomas, we suppose that significant differences might appear if the number of patients increases. We think that the large confidence interval in our box–whisker plot is due to the small number of cases. As often said, SUVmax is a very nonuniform value between institutions. It depends on the dose of radionucleotide that is given, the machine, the timing of scanning and the radiologist reading it and so on. Calculating the SUV tumour mediastinum (T/M) ratio is one of the methods to ensure the universality of SUVmax in [ F] fluoro-2-deoxy-D glucose positron emission tomography-computed tomography (F-FDG PET-CT) [1]. We cannot provide these data in our cohort, as they were not available in our previous cases. However, as other authors have demonstrated [3–5], there is little difference between the results of SUVmax T/M ratio and nonadjusted SUVmax. We believe that nonadjusted SUVmax in F-FDG PET-CT can play an important role in the differential diagnosis between thymomas and thymic carcinomas. The area under the curve in receiver-operating curve for the differential diagnosis between thymomas and thymic carcinomas was 0.951 in our cohort (data is not shown), a result that is considered to be quite good. We completely agree on the necessity of prospective studies with a larger number of patients, as thymic epithelial tumours are quite a rare disease. Discussions between not only thoracic surgeons, but also radiologists and pathologists are required to ensure the universality of radiological and pathological diagnoses.