Patterns of metastasis and recurrence in thymic epithelial tumours: longitudinal imaging review in correlation with histological subtypes

Aim To determine the patterns of metastasis and recurrence in thymic epithelial tumours based on longitudinal imaging studies, and to correlate the patterns with World Health Organization (WHO) histological classifications. Materials and methods Seventy-seven patients with histopathologically confirmed thymomas (n=62) and thymic carcinomas (n=15) who were followed with cross-sectional follow-up imaging after surgery were retrospectively studied. All cross-sectional imaging studies during the disease course were reviewed to identify metastasis or recurrence. The sites of involvement and the time of involvement measured from surgery were recorded. Results Metastasis or recurrence was noted in 24 (31%) of the 77 patients. Patients with metastasis or recurrence were significantly younger than those without (median age: 46 versus 60, respectively; p=0.0005), and more commonly had thymic carcinomas than thymomas (p=0.002). The most common site of involvement was the pleura (17/24), followed by the lung (9/24), and thoracic nodes (9/24). Abdominopelvic involvement was noted in 12 patients, most frequently in the liver (n=8). Lung metastasis was more common in thymic carcinomas than thymomas (p=0.0005). Time from surgery to the development of metastasis or recurrence was shortest in thymic carcinoma, followed by high-risk thymomas, and was longest in low-risk thymoma (median time in months: 25.1, 68.8, and not reached, respectively; p=0.0015). Conclusions The patterns of metastasis and recurrence of thymic epithelial tumours differ significantly across histological subgroups, with thymic carcinomas more commonly having metastasis with shorter length of time after surgery. The knowledge of different patterns of tumour spread may contribute to further understanding of the biological and clinical behaviours of these tumours.