Types

Thymomas display a spectrum of neoplastic behaviours, types A-C : (1)

Thymoma (majority of thymic tumours)

• Type A: medullary, spindle cell
• Type AB: mixed
• Type B1: predominantly cortical, organoid
• Type B2: cortical
• Type B3: well-differentiated thymic carcinoma, squamoid.

Type C represents thymic carcinomas and comprises approximately 15% of thymic neoplasms:

• Tumours with low malignant potential include well-differentiated squamous cell carcinoma, basaloid carcinoma, and muco-epidermoid carcinoma.
• Tumours with more aggressive malignant potential include high-grade lympho-epithelial-like carcinoma, undifferentiated/anaplastic carcinoma, sarcomatoid, and clear-cell carcinomas.

Neuro-endocrine tumours of the thymus (NETT) are extremely rare:

• Small cell carcinoma
• Carcinoid
• Atypical carcinoid.

Reference

1. Marx A, Chan JKC, Chalabreysse L, et al. The 2021 WHO classification of tumours of the thymus and mediastinum: what Is new in thymic epithelial, germ cell, and mesenchymal tumours? J Thorac Oncol. 2022 Feb;17(2):200-13.