Rapidly Enlarging Port-Site Mass after Thoracoscopic Lung Resection: Desmoid-Type Fibromatosis Mimicking Pleural Recurrence

Desmoid-type fibromatosis is a rare, benign fibroblastic neoplasm characterized by infiltrative growth and a tendency for local recurrence despite the absence of metastatic potential. It has been associated with prior trauma or surgery, and postoperative lesions arising in the chest wall can present a major diagnostic challenge. In patients after lung cancer resection, a new pleural-based or chest wall mass at a previous port site is often interpreted as pleural dissemination, chest wall recurrence, or port-site implantation, even when the primary tumor is pathologically low risk. A 70-year-old woman underwent minimally invasive resection for lung adenocarcinoma, and the final pathological stage was pT1miN0M0 (pStage IA1). She remained asymptomatic, and routine postoperative surveillance was performed. At 10 months after surgery, computed tomography revealed a newly developed, well-demarcated soft-tissue mass arising from the chest wall at the thoracoscopic port site, adjacent to the pleura; the mass rapidly enlarged to 3.0 cm by 14 months. Positron emission tomography/computed tomography with fluorine-18 fluorodeoxyglucose showed mild tracer uptake within the lesion (maximum standardized uptake value, 2.5). Although the primary lung adenocarcinoma was pathologically low risk, pleural dissemination or port-site recurrence could not be confidently excluded based on imaging alone. Considering the need for definitive diagnosis and local control, the patient underwent en bloc resection of the lesion with chest wall excision including the seventh rib. Grossly, the tumor was firm and fibrous. Histopathological examination demonstrated a proliferation of bland spindle-shaped cells embedded in abundant collagenous stroma with infiltrative margins, consistent with desmoid-type fibromatosis. The postoperative course was uneventful. As the surgery was performed recently, long-term follow-up data are not yet available. Desmoid-type fibromatosis can occur at a thoracoscopic port site more than one year after lung cancer surgery and may mimic pleural dissemination or port-site recurrence, even after resection of minimally invasive adenocarcinoma. When malignancy cannot be excluded preoperatively, surgical excision with an adequate margin can establish the diagnosis and achieve local disease control.