Thymoma is the most frequent tumor arising in human thymus.

Types

 thymic epithelial tumors

 type A thymoma (spindly thymoma)
 type AB thymoma (mixed thymoma)
 type B thymoma (lymphocyte-rich thymoma)

• type B1
• type B2
• type B3

 ectopic hamartomatous thymoma

Cytogenetics

 chromosome 6 anomalies

• del(6)(p22p25) in type A and type AB thymomas (#14499698#)
• ring chromosome 6

 chromosomes 12 and 16 anomalies

• pseudodicentric (16;12)(q11;p11.2) (type AB or mixed thymoma)

Allelotyping (Loss of heterozygosity (LOH) loci)

• 6q23.3-25.3 (23.5%-45.8%) (#12368223#)
• 3p14.2 (FHIT gene locus)
• 5q21 (APC)
• 6p21
• 6q21-22.1
• 7p21-22
• 8q11.21-23
• 13q14 (RB)
• 17p13.1 (p53)

Tumorigenetic pathways

 APC-associated pathway: 5q21 - 3p22-24.2 - 13q14 - 17p13.1 regions.
 type A thymomas: 6q23.3-25.5 only

Microsatellite instability (MSI)

 microsatellite instability (MSI): 2.4%-12.5% (#12368223#) .

• type B3 thymoma only (?)