Discussion
Thymic neoplasms are very rare tumours in pediatric patients. Present literature concerning thymic tumours is mostly comprised of single case reports with only few larger series [2-9]. Diagnosis, as in adults, is made after biopsy or tumour resection, but could be difficult due to the rarity of this tumour in pediatric population. Differential diagnosis of mediastinal mass usually reveals lymphoma or neurogenic tumours [4]. Patients presents with nonspecific symptoms of airway obstruction which was also observed in our study although not all of the patients had disease signs [1-9]. None of children presented with myasthenia gravis, but the coexistence of it with thymoma in children is less frequent with incidence of 7 to 15% [2,3,14,15]. WHO histopathological classification and Masaoka-Koga staging systems are the basis for treatment choice in adults as well as in children [10-12].
Fonseca AL. et al. in her report described the results of thymic tumours in children and found that this tumours presents more often in male but our group shows no sex predominance [15]. The largest study of Stachowicz-Stencel of 36 thymoma and thymic carcinoma patients showed male predominance – 21 male vs 15 female patients, also Rod J. in his literature analysis found male predominance in pediatric thymoma population [2,3]. Median age of patient described in our study is younger than reported in literature (median 12 years old) [2,3].
Surgery, possibly with R0 resection, remains the gold standard for treating all thymic neoplasms. CTH and RTH are used in patients with large or inoperable tumours, in the presence of metastases or after non-radical resections [1-3,5-9] (Table 5). Thymic carcinoma carries more poor prognosis and chemoradiotherapy is often offered after resection [2,3,6]. RT doses used in other studies usually are within the range of 40 to 54 Gy, which corresponds to the total doses used in majority of our patients [1-9]. Very young age could be the reason for implementing doses below 40 Gy in our group. A report from the European Cooperative Study Group for Pediatric Rare Tumors (EXPeRT) written by Stachowicz-Stencel T. et al described results of 16 patients with thymoma and 20 with thymic carcinoma [2]. Only one child with thymoma received RTH and at the end of median follow-up of 5 years only 2 patients (12.5%) died due to the disease. Cisplatin was the most commonly used systemic agent, but only 4 patients received CTH. What is important, radical surgery (R0) was achieved in 11 of them and was the only treatment in those patients. Thymic carcinoma patients in majority had only biopsy (80%), received CTH (70%) and RTH (60%) with total dose of 38 to 54 Gy which could translate into such poor results of 5-year OS of only 21% [2]. The same observation could be made based on Ramon y Cajal S et al. study with median survival of patients with thymic carcinoma of only 8 months [8]. Also Rod et al. in the report from French Society of Pediatric Oncology observed poor results in patients with thymic carcinoma [3]. The patient with thymic carcinoma included in our analysis had radical surgery and received postoperative RTH to 44 Gy which resulted in 74-month free of disease follow-up.
The limitations of our study are like in all studies on rare tumours - a retrospective study covering a long time period with different treatment modalities. Although, due to the rarity of this tumour in pediatric population, studies like ours are the only way to collect the experience in this topic.
Combined treatment, including surgery, chemotherapy and radiotherapy could provide satisfactory results in thymoma patients. There is need for further larger multi-national or institutional analysis with long-term follow-up which can help to provide more information for optimal management strategies and outcome.
Conflict of interest : The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Authors’ contributions : Conceptualization, A.N., L.M.; methodology, A.N.; software, A.N.; formal analysis, A.N.; investigation, A.N.; resources, A.N.; data curation, A.N.; writing—original draft preparation, A.N.; writing—review and editing, A.N., L.M..; visualization, A.N.; supervision, L.M. All authors have read and agreed to the published version of the manuscript.
Acknowledgment: Not applicable.