Radiation Oncology/Thymoma/Staging

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Thymoma Staging

  • There is no universally accepted system; no AJCC staging existed before the 8th edition, which will go into effect January 1st, 2018 in the United States
  • Historically, a classifiaction system used both histological features and clinical behavior
  • Masaoka staging is the clinically used staging system, although it may not be predictive for thymic carcinoma
  • GETT staging is the surgical staging system, and may have better correlation with outcome
  • A meta-analysis from UCLA suggests that evaluation of transcapsular extension (Stage I vs. Stage IIa) is of no clinical value, as they have same DFS and OS outcomes

Historical Classification

  • Benign Thymoma (histologically and behaviorally benign)
  • Malignant Thymoma (invasive)
    • Type I - histologically benign, but behaving aggressively with local invasion
    • Type II ("thymic carcinoma") - histologically malignant, aggresive behavior

Masaoka TNM Staging (1999) - PMID 10047676

Stage Description
T1 Macroscopically completely encapsulated AND microscopically no invasion
T2 Invasion into or through the capsule
T2a Microscopic invasion into capsule
T2b Macroscopic adhesion, or invasion into surrounding fatty tissue, or mediastinal pleura
T3 Invasion into neighboring organs
T3a No invasion of great vessels
T3b Invasion of great vessels
T4 Pleural or pericardial dissemination
N Lymph node status
N1 Anterior mediastinal LNs
N2 Intrathoracic LNs except anterior mediastinal LNs
N3 Supraclavicular LNs
M0 Metastatic status
M1 Hematogenous metastasis or extrathoracic LNs except supraclavicular LNs

Original Masaoka Staging (1991) - PMID 1913546

  • Stage I - Macroscopically and microscopically completely encapsulated
  • Stage II - Macroscopic invasion into surrounding fatty tissues or mediastinal pleura or microscopic invasion into the capsule
  • Stage III - Macroscopic invasion into adjacent organs or intrathoracic metastases
  • Stage IVA - Pleural or pericardial implants/dissemination
  • Stage IVB - Nodal or hematogenous metastases

GETT Staging

  • Stage IA - Encapsulated, completely resected
  • Stage IB - Macroscopically completely resected but suspicion of mediastinal adhesions or potential capsular invasion at surgery
  • Stage II - Invasive tumor, completely resected
  • Stage IIIA - Invasive tumor, subtotal resection
  • Stage IIIB - Invasive tumor, biopsy alone
  • Stage IVa - Supraclav or pleural met
  • Stage IVb - Distant metastases