Risk factors and prognostic factors of pleural metastases in thymic epithelial tumors: A narrative review.

Introduction: Pleural metastases are common in thymic epithelial tumors (TET), which include pleural recurrence and stage IVa at initial diagnosis. However, the specific risk factors predicting its recurrence (i.e., pleural recurrence group) and prognostic factors for pleural metastasis (i.e., stage IVa) remain unclear. This review aims to identify and discuss the predictors associated with pleural metastases in patients with TET.

Methods: A systematic literature search was conducted on PubMed, MEDLINE, Embase, and Cochrane for articles published between 1/1/1990 and 3/11/2023. The selection process was independently carried out by three researchers, and the quality of the selected papers was assessed using the Newcastle-Ottawa Scale (NOS).

Results: Out of the 4932 papers reviewed, 22 were included in the final analysis: 15 papers on risk factors of pleural recurrence after primary treatment(i.e., recurrence group) and 7 papers on the prognostic factors of patients with stage IVa at diagnosis(i.e., stage IVa group). Of the 15 former articles, 5 identified pleural invasion and invasion of other tissues as significant risk factors for pleural recurrence. Four of 15 papers identified the Masaoka-Koga stage as a significant risk factor, while two of 15 papers identified the contact length between the tumor contour and the lung as a contributing factor for pleural recurrence. Additionally, two papers suggested that tumor size may be a risk factor for pleural recurrence. Six other papers discussed various factors, including a lobulated tumor contour, WHO histologic classifications B2 and B3, radiotherapy doses of≤50Gy, incomplete resection, and Entire hemithorax radio therapy, as potential risk factors. Furthermore, one paper specifically addressed the decreased risk for pleural dissemination associated with Video-Assisted Thoracoscopic Surgery (VATS) thymectomy. In patients with stage IVa at diagnosis group, three of 7 papers mentioned that resection influenced the prognosis. Two papers discussed the number of nodules in the pleura but arrived at different conclusions. One paper suggested that patients older than 50 years might have worse outcomes, while another analyzed the invasion of structures but did not find any significant results.

Conclusion: For pleural recurrence patients, the most commonly discussed risk factor is pleural invasion. Other identified risk factors include the Masaoka-Koga stage, contact length between the tumor contour and the lung, tumor size, lobulated tumor contour, WHO histologic classifications B2 and B3, radiotherapy doses of≤50Gy, and incomplete resection. For patients with stage IVa at diagnosis, non--extrapleural pneumonectomy, incomplete or no resection, and histological subtype may contribute to a poorer prognosis in patients diagnosed with pleural dissemination. The number of disseminated pleural nodules remains controversial and may be correlated with resectability.