Table 1 shows the background information of all patients. The cohort included 30 males and 30 females with a mean age of 61 years (range: 25–82 years). Moreover, the mean duration of the postoperative follow-up period was 81 months; only deaths caused by the primary disease were considered cases of mortality in this study.
Surgical treatment and perioperative period
Median sternotomy, lateral thoracotomy, the clamshell approach, and the complete thoracoscopic approach were employed in 39, one, five, and 15 patients, respectively. Additionally, 17 patients underwent extended thymectomy, while 43 underwent thymomectomy (Table 1).
Additional combined resection of adjacent organs was performed in eight patients; of these patients, six, four, one, and one underwent resection of the lung, pericardium, superior vena cava, and diaphragm, respectively. No perioperative mortality was observed, but 10 patients (16.7%) developed postoperative complications including myasthenic crisis (n = 2), Horner’s syndrome (n = 1), chylothorax (n = 1), respiratory failure (n = 2), phrenic nerve palsy (n = 3), and postoperative failure of the sternal closure (n = 1).
Stage classification, therapeutic modalities, and patient prognoses
Among the 60 patients with thymomas, 47, four, three, four, and two had tumors of stages I, II, III, IVa, and IVb, respectively (Table 1). The overall five-year survival and recurrence-free survival (RFS) rates were 96% and 86%, respectively. Among patients with stage I, II, and III thymomas, no cases of mortality were observed during the follow-up period. The five-year survival rates of those with stage IVa and IVb thymomas were 100% and 0%, respectively (Fig. 1a). Although the five-year survival rate of patients with stage IVa thymomas was 100%, one of the four patients died of intrathoracic disseminated recurrence 123 months after surgery, while two patients with stage IVb tumors died of pleural disseminated recurrence 21 and 42 months after surgery, respectively. Meanwhile, the five-year RFS rates in stage I, II, III, IVa, and IVb tumors were 100%, 75%, 67%, and 0%, respectively (Fig. 1b). Patients with stage I or II tumors and III or IV tumors demonstrated five-year RFS rates of 100% and 78%, respectively; therefore, stage III and IV thymomas were associated with a significantly poorer prognosis (p < 0.001) (Table 2). The five-year survival rate among the patients who underwent incomplete resection (71%) was significantly lower than that among those who underwent complete resection (100%), indicating a poorer prognosis in the latter group (p < 0.001) (Fig. 2).
Prognostic evaluation based on the WHO classification
According to the histological type (WHO classification), the cohort included six, 14, 11, 22, and seven thymomas of types A, AB, B1, B2, and B3, respectively. Additionally, the five-year survival rates for types A, AB, B1, B2, and B3 were 100%, 100%, 86%, 100%, and 86%, respectively (Fig. 3a). The corresponding five-year RFS rates were 100%, 91%, 91%, 81%, and 71%, respectively (Fig. 3b).
Autoimmune complications of thymomas
The autoimmune complications of thymomas included myasthenia gravis, pure red cell aplasia, and lichen planus in 10, one, and one case(s), respectively. Overall, autoimmune complications were observed in one (17%), one (7%), four (36%), seven (31%), and zero (0%) cases with types A, AB, B1, B2, and B3 tumors, respectively. The presence of autoimmune complications was significantly higher among patients with thymomas of types B1 and B2. Myasthenia gravis did not affect the prognosis of patients with thymomas (Table 2).
Treatment for recurrence and postoperative prophylactic treatment
Overall, six, one, and one patient(s) developed pleural dissemination, local mediastinal lesions, and lung metastasis during initial recurrence, respectively; thus, pleural dissemination was the most common postoperative complication. Surgical resection for pleural dissemination was performed in one recurrent case.
The most frequently used chemotherapeutic regimen for the treatment of recurrence was adriamycin + cisplatin + vincristine + cyclophosphamide (ADOC), followed by carboplatin (CBDCA) + paclitaxel (PTX) and cisplatin + etoposide, respectively. After undergoing initial surgery for the primary lesion, three patients received prophylactic ADOC, while one received CBDCA + PTX chemotherapy.
Post-recurrence radiotherapy was administered to four cases with pleural dissemination, while three (6%), two (50%), two (67%), and five (83%) patients with stages I, II, III, and IV thymomas received postoperative prophylactic radiotherapy, respectively. One patient with stage IV thymoma refused postoperative prophylactic radiotherapy.
Prognostic evaluation based on the recurrence-free period
The recurrence-free period was less than three years and three years or more in six and two recurrent cases, respectively. The corresponding five-year RFS rates were 83% and 100%, respectively, indicating a poorer prognosis in patients with a recurrence-free period of less than three years, compared to three years or more (Table 2, Fig. 4).