Thymic epithelial malignancies are rare tumors. There have been many obstacles to progress in these diseases. Among these has been the lack of an official, consistent stage classification system put forth by the American Joint Committee on Cancer (AJCC) and the Union for International Cancer Control (UICC) —the bodies responsible for defining stage classification throughout the world. At least 15 different stage classification systems have been proposed and used.¹ x 1 Filosso, P, Ruffini, E, Lausi, P, Lucchi, M, Oliaro, A, and Detterbeck, F. Historical perspectives: the evolution of the thymic epithelial tumors staging system. Lung Cancer. 2014; 83: 126–132 Abstract | Full Text | Full Text PDF | PubMed | Scopus (27) | Google Scholar See all References These have been largely empirically derived, based on data from small numbers of patients. Perhaps the most widely used have been the Masaoka classification (derived from data on 91 patients),² x 2 Masaoka, A, Monden, Y, Nakahara, K, and Tanioka, T. Follow-up study of thymomas with special reference to their clinical stages. Cancer. 1981; 48: 2485–2492 Crossref | PubMed | Scopus (1191) | Google Scholar See all References and the Koga modification of this (based on 76 patients).³ x 3 Koga, K, Matsuno, Y, Noguchi, M et al. A review of 79 thymomas: modification of staging system and reappraisal of conventional division into invasive and non-invasive thymoma. Pathol Int. 1994; 44: 359–367 Crossref | PubMed | Scopus (211) | Google Scholar See all References Even among centers using one of these classification systems, often the definitions have been interpreted differently because of vague wording, thus hampering the ability to collaborate effectively.⁴ x 4 Detterbeck, FC, Moran, C, Huang, J et al. Which way is up? Policies and procedures for surgeons and pathologists regarding resection specimens of thymic malignancy. J Thorac Oncol. 2011; 6: S1730–S1738 Abstract | Full Text | Full Text PDF | PubMed | Scopus (63) | Google Scholar See all References

A retrospective database was developed by the European Society of Thoracic Surgeons, collecting patients submitted to surgery for thymic tumours to analyse clinico-pathological prognostic predictors. A total of 2151 incident cases from 35 institutions were collected from 1990 to 2010. Clinical-pathological characteristics were analysed, including age, gender, associated myasthenia gravis stage (Masaoka), World Health Organization histology, type of thymic tumour [thymoma, thymic carcinoma (TC), neuroendocrine thymic tumour (NETT)], type of resection (complete/incomplete), tumour size, adjuvant therapy and recurrence. Primary outcome was overall survival (OS); secondary outcomes were the proportion of incomplete resections, disease-free survival and the cumulative incidence of recurrence (CIR). A total of 2030 patients were analysed for OS (1798 thymomas, 191 TCs and 41 NETTs). Ten-year OS was 0.73 (95% confidence interval 0.69–0.75). Complete resection (R0) was achieved in 88% of the patients. Ten-year CIR was 0.12 (0.10–0.15). Predictors of shorter OS were increased age (P < 0–001), stage [III vs I HR 2.66, 1.80–3.92; IV vs I hazard ratio (HR) 4.41, 2.67–7.26], TC (HR 2.39, 1.68–3.40) and NETT (HR 2.59, 1.35–4.99) vs thymomas and incomplete resection (HR 1.74, 1.18–2.57). Risk of recurrence increased with tumour size (P = 0.003), stage (III vs I HR 5.67, 2.80–11.45; IV vs I HR 13.08, 5.70–30.03) and NETT (HR 7.18, 3.48–14.82). Analysis using a propensity score indicates that the administration of adjuvant therapy was beneficial in increasing OS (HR 0.69, 0.49–0.97) in R0 resections. Masaoka stages III–IV, incomplete resection and non-thymoma histology showed a significant impact in increasing recurrence and in worsening survival. The administration of adjuvant therapy after complete resection is associated with improved survival.