Anterior mediastinal lesions smaller than 3 cm detected during lung cancer screening may be managed safely with annual imaging surveillance rather than immediate referral if they lack concerning radiologic features.

Researchers conducted a retrospective analysis of the prospective SUMMIT lung cancer screening study involving 12,961 current or former smokers aged 55 to 77 years from North-East and Central London who underwent low-dose computed tomography (LDCT) screening between April 2019 and June 2021. Patients with anterior mediastinal lesions measuring 3 cm or larger at baseline, demonstrating concerning radiologic features, or showing interval growth were referred for multidisciplinary evaluation. Patients with lesions smaller than 3 cm without concerning features underwent annual LDCT surveillance for up to two years. Outcomes were assessed using follow-up LDCT imaging, electronic health records, and the UK National Cancer Registration and Analysis Service.

The primary objective was to determine whether a conservative management strategy for anterior mediastinal lesions smaller than 3 cm was safe. Secondary objectives included determining the prevalence of screen-detected anterior mediastinal lesions and describing the outcomes of patients referred for additional evaluation.

Anterior mediastinal lesions were identified in 91 of 12,961 screened patients, corresponding to a baseline prevalence of 0.7%. Most lesions (68%) measured less than 3 cm at baseline.

Among the 54 patients with lesions smaller than 3 cm who underwent annual follow-up, 74% completed two years of follow-up without requiring referral for further assessment. Fourteen patients were referred after interval growth was detected on follow-up imaging, and four were diagnosed with thymoma following surgical resection. One patient required adjuvant radiotherapy following an incomplete resection.

Overall, 16 patients underwent surgical resection, resulting in eight thymoma diagnoses and eight benign lesions, yielding a benign resection rate of 50%. Three of the thymomas were classified as type B2 tumors. The researchers also reported that most confirmed thymomas appeared homogeneous on LDCT and were rounded or lobulated. During a median follow-up of nearly 2,000 days, no thymic or anterior mediastinal malignancies were diagnosed among patients with lesions smaller than 3 cm who completed surveillance without referral.

The researchers also found that most anterior mediastinal lesions were largest in the cranio-caudal plane, emphasizing the importance of reviewing sagittal images to avoid underestimating lesion size during assessment.

The study had several limitations. The retrospective observational analysis included relatively few anterior mediastinal lesions, and tissue confirmation was available for only 16 surgically resected lesions. The duration of imaging follow-up was relatively short given the natural history of thymoma, and lesion growth and morphology were assessed subjectively without measuring interobserver variability. The researchers emphasized that the study was designed to evaluate the safety of a pragmatic referral strategy rather than determine whether the 3-cm threshold distinguishes benign from malignant lesions.

The findings suggest that selected patients with anterior mediastinal lesions smaller than 3 cm may undergo surveillance rather than immediate referral within lung cancer screening programs, although additional studies with larger cohorts and longer follow-up are needed to further evaluate this approach.

"Our analysis suggests that, in the absence of concerning LDCT features, a 3 cm baseline diameter referral threshold for screen-detected anterior mediastinal lesions is safe, enabling most participants to continue surveillance within the screening programme without compromising on clinical outcomes," wrote lead study author Amyn Bhamani, of the Lungs for Living Research Centre, University College London, and colleagues.

Disclosures: The study was funded by GRAIL, Inc. Several authors reported financial relationships with industry, including employment, research funding, consulting, advisory roles, honoraria, and travel support, as detailed in the published article.

Source: European Radiology