Benign Tumor at a Lung Surgery Port Site Fooled Doctors Into Fearing Cancer Recurrence

A 70-year-old woman who had undergone minimally invasive surgery for a very early-stage lung adenocarcinoma developed a rapidly growing mass at one of her thoracoscopic port sites, and the lesion looked so much like spreading cancer that her surgical team felt compelled to remove it entirely. The final diagnosis, however, was not malignancy at all: the mass turned out to be desmoid-type fibromatosis, a rare, benign fibroblastic tumor that never metastasizes but grows in an infiltrative pattern and has a well-known tendency to come back locally. The case, published as a case report in the journal General Thoracic and Cardiovascular Surgery Cases, illustrates a genuine diagnostic pitfall in postoperative surveillance after lung cancer surgery, because a new, enlarging, pleura-adjacent chest wall mass at a previous port site is exactly where surgeons expect to see recurrence or tumor seeding.

The original operation had been a sublobar resection performed through a three-port video-assisted thoracoscopic approach, with a utility incision of up to 4 centimeters and two additional port incisions of roughly 2 centimeters each. Preoperative computed tomography had shown a small pulmonary lesion, and the final pathological diagnosis was minimally invasive adenocarcinoma staged pT1miN0M0, corresponding to pathological stage IA1. That is about as favorable a lung cancer diagnosis as a patient can receive. The woman’s postoperative course was uneventful, she remained asymptomatic, and she entered routine surveillance imaging, the standard pathway for patients whose tumors carry such a low risk of returning.

Ten months after the surgery, computed tomography revealed a newly developed soft-tissue lesion in the chest wall, adjacent to one of the prior thoracoscopic port sites and abutting the pleura, the delicate membrane lining the chest cavity. The patient had no symptoms, and laboratory tests showed nothing suggestive of infection. Over the following months the lesion enlarged progressively, reaching 3.0 centimeters by 14 months after the original operation. Upright chest radiography and contrast-enhanced computed tomography confirmed a well-demarcated chest wall mass pressing against the pleura at the port site. The growth kinetics alone were alarming: a mass that appears within a year of lung cancer resection and then steadily enlarges is, by default, treated as suspicious.

The imaging workup could not resolve the ambiguity. Positron emission tomography combined with computed tomography, using fluorine-18 fluorodeoxyglucose as the radioactive tracer, showed only mild uptake within the lesion, with a maximum standardized uptake value of 2.5. That number sits in an uncomfortable middle ground. Intensely glucose-avid lesions raise strong suspicion of malignancy, but mild uptake neither excludes cancer nor rules out desmoid-type fibromatosis, which can itself display low-to-moderate tracer uptake. In other words, the scan was compatible with several possibilities at once: benign postoperative change, desmoid fibromatosis, pleural dissemination of the original adenocarcinoma, chest wall recurrence, or implantation of tumor cells at the port site during the initial operation.

The authors of the report emphasize why this uncertainty is so difficult to manage clinically. Although minimally invasive adenocarcinoma generally carries an excellent prognosis, rare recurrences have been reported even in patients staged pT1miN0M0, including cases of pleural disease confirmed as metastasis through comprehensive cancer gene panel analysis. Clinicians therefore face a balancing act between the low pretest probability of recurrence in a pathologically low-risk tumor and the potentially serious consequences of missing an early relapse. Imaging alone, the report concludes, may be insufficient to distinguish benign postoperative processes from malignant recurrence, particularly when interval growth is observed over serial scans.

Faced with a lesion that could not be characterized definitively, the surgical team chose an approach designed to protect against both possibilities at once. To minimize any potential tumor seeding, they created a new thoracoscopic port at a site distant from the chest wall mass. Through that port they inspected the pleural cavity and visualized the chest wall lesion from the intrathoracic side. No additional pleural nodules were seen and there was no malignant-appearing pleural effusion, both reassuring findings. Nevertheless, because pleural dissemination or port-site recurrence still could not be definitively excluded on the basis of the overall picture, the team planned a no-touch en bloc resection, a technique in which the tumor is removed in one piece without ever being directly manipulated.

That operation involved a skin incision directly over the lesion and excision of the tumor together with a segment of chest wall, including the seventh rib. Chest wall excision including a rib, the authors note, is reasonable when adequate margins are required or when the tumor appears inseparable from the chest wall structures. The resected specimen was firm and fibrous on gross examination. Under the microscope, the tissue showed bland spindle-shaped cells arranged in long fascicles within an abundant collagenous stroma, growing with infiltrative margins. Immunohistochemistry added two decisive pieces of information: the tumor cell nuclei were positive for β-catenin, a characteristic finding that supports the diagnosis of desmoid-type fibromatosis, and the cells were also positive for α-smooth muscle actin, consistent with myofibroblastic differentiation. Together these features established the diagnosis, and all surgical resection margins proved histologically negative for tumor, meaning the excision was complete, an R0 resection.

The diagnosis matters because desmoid-type fibromatosis behaves in a paradoxical way. It is biologically benign, with no metastatic potential whatsoever, yet it is locally aggressive, infiltrating adjacent structures and recurring after incomplete removal. It can arise sporadically and has also been associated with prior trauma or surgical intervention, which is precisely why it can appear at a surgical port site months to years after an operation. Management of the disease has in recent years shifted toward active surveillance for asymptomatic, stable lesions, reflecting growing recognition that many desmoids can be watched rather than cut out. But the authors argue that observation may be inappropriate in a postoperative lung cancer patient when malignancy cannot be excluded and the lesion is actively enlarging. In their patient, the mass was detected at 10 months, had grown to 3 centimeters by 14 months, and its port-site location and pleural adjacency raised concrete concern for dissemination or port-site recurrence, so en bloc resection served the dual purpose of establishing the diagnosis and achieving local control.

The case carries a broader message for surveillance imaging after lung cancer surgery. A growing, pleural-adjacent chest wall mass at a thoracoscopic port site triggers an immediate assumption of malignancy, and the authors argue that desmoid-type fibromatosis should be added to the differential diagnosis in that setting, even after resection of a minimally invasive adenocarcinoma. When malignancy cannot be excluded preoperatively, surgical excision with an adequate margin can both settle the question and provide local disease control. The report also carries the standard caveats of a single-case publication: it describes one patient’s experience rather than a systematic study, and because the definitive surgery was performed recently, no long-term follow-up data are yet available to confirm that the lesion will not recur locally. The authors accordingly recommend careful postoperative surveillance and longer follow-up, noting that even though desmoid-type fibromatosis lacks metastatic potential, local recurrence remains possible.

For patients and clinicians alike, the takeaway is a lesson in diagnostic humility. The authors’ assessment should integrate oncologic background, growth kinetics, the anatomic relationship to the pleura and surgical tract, and the feasibility of obtaining a definitive diagnosis, rather than relying on any single imaging finding.

Subject of Research: Desmoid-type fibromatosis arising at a thoracoscopic port site after lung cancer resection and mimicking pleural recurrence

Article Title: Rapidly enlarging port-site mass after thoracoscopic lung resection: desmoid-type fibromatosis mimicking pleural recurrence

Article References: Kamimura, G., Aoki, M., Matsushita, T., Imamura, S., Morizono, S., Nonaka, Y., Takeda, A., Maeda, K., Nagata, T., & Ueda, K. (2026). Rapidly enlarging port-site mass after thoracoscopic lung resection: desmoid-type fibromatosis mimicking pleural recurrence. General Thoracic and Cardiovascular Surgery Cases, 5(1), Article 36. https://doi.org/10.1186/s44215-026-00270-5

Image Credits: AI Generated

DOI: 10.1186/s44215-026-00270-5

Keywords: desmoid-type fibromatosis, lung adenocarcinoma, thoracoscopic surgery, port-site mass, pleural recurrence, chest wall tumor, PET-CT imaging, beta-catenin, case report, surgical resection, postoperative surveillance, benign tumor