ESTRO 2024 - Abstract Book

S1709

Clinical - Lung

ESTRO 2024

Purpose/Objective:

Thymomas are the most common primary tumour in the anterior mediastinum, with an annual incidence of 0.18 per 100.000 in Europe 1 . Thymomas are typically slow growing tumours that spread by local extension. Metastases are usually confined to the pleura, lung, pericardium or diaphragm, although extrathoracic metastases are rare. Surgical resection is the mainstay of treatment for thymoma 2,3 . Adjuvant radiotherapy is indicated for most patients undergoing resection for stage IIB, III and IV thymoma 4 .

The aim of this study was to determine overall survival (OS) and distant metastasis-free survival (DMFS) in patients treated with postoperative radiotherapy (PORT) for thymoma.

Material/Methods:

Patients with a histologically confirmed diagnosis of thymoma treated with surgery and postoperative radiotherapy between 1999 and 2022 were included. Stage was defined according to the Masaoka-Koga system. Histological classification was performed according to WHO criteria. Complete resection with negative surgical margins was defined as R0, incomplete resection with microscopic remnants as R1, and subtotal resection with gross remnants as R2. Adjuvant radiotherapy dose was determined according to margin status: R0: 45-50 Gy, R1: 54 Gy and R2: 60 Gy. The fractionation scheme was 1.8-2 Gy. Since 2010, we have been using planning PET-TAC. Adjuvant chemotherapy consisted of cisplatin, cyclophosphamide and doxorubicin. Radiation morbidity was assessed using the RTOG/EORTC acute and late morbidity score. Distant metastasis-free survival was calculated from the date of first radiotherapy to the date of distant relapse, and OS was calculated from the date of first radiotherapy to the last follow-up or to the date of death from any cause.

All statistical analyses were performed with SPSS, version 23.0 (SPSS, Inc., Chicago, IL).

OS and DMFS estimates were generated using the Kaplan-Meier method, and comparisons were made using the log-rank test.

Results:

A total of 31 patients with thymoma were treated with PORT at our centre.

The mean age was 61 years (range 35-80), with fifteen females and sixteen males. Five patients had myasthenia gravis at diagnosis. Fifty-five percent of the patients were asymptomatic and were diagnosed by an incidental mass on a screening chest radiograph or CT. The median tumour size was 6 cm (range 2.5-15). Masaoka-Koga stages were: IIA: 5, II B: 16, III: 6, IVA: 4. WHO histological subtypes: Favourable (A1: 2, AB: 10, B1: 3) and unfavourable (B2: 10, B3: 6). All patients underwent surgery. The type of resection was R0 in 61% of patients. Four patients were treated with adjuvant chemotherapy. Three-dimensional conformal radiotherapy (3D-CRT) was used in 12 patients and intensity-modulated radiotherapy (IMRT) in 19 patients (tomotherapy: 15, volumetric modulated arc therapy (VMAT): 4).

Mean follow-up was 103 months (range 12-269). Five- and 10-year OS and DMFS were 93% and 66% and 73% and 73%, respectively. Only one patient had a local recurrence.