Different Patterns of Pneumothorax in Patients With Soft Tissue Tumors Treated With Pazopanib

Abstract Background: To investigate the patterns of pneumothorax in pazopanib treatment, focusing on the positional relationship between the visceral pleura and metastatic lung tumor. Methods: We examined 20 patients with advanced soft tissue tumor who developed lung metastases before pazopanib treatment during 2012–2019. Pneumothorax was classified into two types based on the location of the metastatic lesion around the visceral pleural area before pazopanib treatment: subpleural type, within 5 mm from the pleura; central type, > 5 mm from the pleura. We investigated the rates of pneumothorax and the risk factors. Results: Overall, 5 patients experienced pneumothorax (3 subpleural and 2 central type). Cavitation preceded pneumothorax in 80% of the patients and led to connection of the cavitated cyst of the metastatic lesion to the chest cavity in a shorter term in those with the subpleural type. Conversely, a more gradual increase in cavity and sudden cyst rupture were observed in the central type. The risk factors for pneumothorax were cavitation after the initiation of pazopanib and previous intervention before pazopanib including ablation or surgery. The locations of metastatic lesion were not risk factor for the occurrence of pneumothorax.Conclusion: Pneumothorax is an adverse event of pazopanib treatment. Therefore, attention must be paid to the predisposing factors such as the formation of cavitation after pazopanib initiation and previous interventions on the lungs. Moreover, as the subpleural pneumothorax tends to occur earlier than the central type, the different time course can be anticipated based on the positional relationships of the metastatic lesions to the visceral pleura.