Locally advanced thymoma treated with lattice radiotherapy: a case report

Background: Complete resection is the optimal treatment for thymoma, but is challenging in bulky tumors. Adequate neoadjuvant chemoradiation becomes crucial, although its safety and efficacy must be carefully weighed, particularly for high-volume disease. Downstaging tumor or providing durable local control can be challenging. Lattice radiotherapy (LRT) is a form of spatially fractionated radiotherapy (SFRT) that offers a dual benefit of cytotoxic effects and immunogenic cell death, making it a promising approach in the neoadjuvant treatment of bulky tumors. We present the first case of advanced thymoma undergoing LRT followed by complete surgical resection. Case Description: A 50-year-old Taiwanese woman presenting with dyspnea was diagnosed with a 17 cm, cT3N0M1b, modified Masaoka stage IVB thymoma, metastatic to lung. After three cycles of etoposide and cisplatin, she underwent concomitant chemotherapy (one cycle of etoposide and cisplatin and one cycle of paclitaxel and carboplatin) with LRT. A single fraction of 20 Gy was delivered to vertices within the tumor, then the entire tumor was treated with 45 Gy in 25 fractions. She tolerated the treatment without significant acute toxicity. She then underwent radical resection of the primary tumor without nodal dissection, achieving clear margins and a final pathological stage of ypT1aNx. Follow-up computed tomography (CT) at five months post-operation did not find local recurrence. No symptomatic subacute radiation toxicity affecting the heart or lungs was observed. Conclusions: We have safely delivered LRT as part of neoadjuvant concurrent chemoradiation to a patient with large thymoma. This technique may have the potential to improve resectability and response rate of bulky tumors.