Methods
A retrospective study of patients with thymic tumours treated in our Institution between 1985 and 2019 was performed. All consecutive patients with thymic tumours younger than 18 years old were included into the study.
The following parameters were included in the analysis: date of diagnosis, primary tumour characteristics, given curative treatment, performance status, systemic therapy, RTH characteristics - total dose, irradiated volume, early and late toxicity, local response, date and reason of death. Missing dates of deaths were obtained from the Polish National Cancer Registry.
The criteria for diagnosing thymoma or thymic carcinoma used were as established by the WHO classification [10] (Table 1). Tumours were staged according to the commonly-used Masaoka-Koga staging system [11,12] (Table 2). Eastern Cooperative Oncology Group (ECOG) scale was used to classify patients’ performance status. EORTC/RTOG toxicity criteria were used to assess treatment morbidity [13]. Tumour response was classified, as follows: complete regression (CR) was defined as complete disappearance of all clinical and radiological evidence of the disease, partial regression (PR) as a decrease of tumour size in clinical or radiologic evaluation and progression as increase in lesion size or occurrence of new lesions.
Median follow-up was estimated by Kaplan-Meier analysis with the reversed meaning of the status indicator. Overall survival (OS) was calculated from the date of disease diagnosis to the date of last follow-up or death. Progression free survival (PFS) was calculated from the date of diagnosis to the date of local/distant progression or death. The Kaplan-Meier method was used to estimate survival. Statistical analyses were performed using Statistica 12.0.
A total number of 8 children (4 boys and 4 girls) with thymic tumours were identified. Median age at diagnosis was 7 years (range 1 to 18). In all the cases, the diagnosis was based on diagnostic imaging and pathologic examination of the tumour tissue samples obtained during the surgery. In 4 cases, tumour was found on a computed tomography (CT) of the chest and in 4 cases (treated in the earlier years of a study) on the chest X-ray. Mean tumour dimensions were 82 x 62 x 93 mm and the tumours ranged from 50 to 135 mm in the greatest dimension. In 3 patients tumour showed contrast enhancement, in 4 cases tumour was constricting nearby organs and in 1 case infiltration of surrounding tissues was described. In one patient lung metastases were diagnosed simultaneously with primary tumour.
All patients had histopathologic confirmation of thymic neoplasm – in 7 of them thymoma was diagnosed, in 1 thymic carcinoma. In 5 of them WHO type was assessed – in two of them B1 type was found, in one B2, in one AB and in one C. Tumours were staged according to the commonly-used Masaoka-Koga staging system in 5 cases – stage II in one, stage III in three and stage IV in one.
ECOG scale was used to classify patients’ performance status and all but one patient were in a good performance status at the time of the diagnosis (ECOG 0-1). Symptoms of the disease were present in 5 of them and lasted for 1 to 24 months – weakness in 3 of them, dyspnea in 1, cough in 2, weight loss in 2 and fever in 2. Other symptoms presented individually were: doubled vision, oedema of the neck and face and palpable neck tumour. In one patient diagnostic was introduced due to the lung infection. None of them presented with myasthenia.
All the patients were treated with radical intention. The characteristics of the treatment used in particular patients are presented in Table 3. In all but one surgery was the first-line treatment, however only in two cases a complete removal of the tumour was performed and other patients had partial resection. One patient started treatment with CTH and four others received CTH after the surgery. In one patient CTH was combined with RTH. Systemic treatment applied was: ADOC (doxorubicin 40mg/m2 + cisplatin 50mg/m2 + vincristine 0.6mg/m2 + cyclophosfamid 700mg/m2) – in 3 patients; cisplatin + adriamicin + bleomycin + encorton in 2 patients, VIP (etoposide 75mg/m2 + cisplatin 20mg/m2 + ifosfamide 1.2g/m2) in 1 patient and PACE (cisplatin 50mg/m2 + doxorubicin 50mg/m2 + cyclophosfamid 500mg/m2) in 1 patient. In 2 of them ADOC was followed by VIP and in one by cisplatin + adriamicin + bleomycin + encorton. Usually six cycles of CTH was applied.
RTH was applied to median total dose of 37.5 Gy. Radiotherapy characteristics is presented in Table 4. In all patients conformal technique (two or three fields’ technique) was used. Irradiated volume (CTV, clinical target volume) included mediastinum in 4 patients combined with boost on lung metastasis in stage IV patient and with tumour bed boost and chest lymph nodes irradiation in 1 patient, tumour in 1 patient and tumour bed in 1 patient. Planned target volumes (PTVs) were created by adding additional margins to CTV in order to correct for inaccuracies in the delivery system (set-up margins) or interfraction and intrafraction of organ motions.