lipomas

Digital slides

 UI:849 - soft tissue lipoma

Images

 endobronchial lipoma

• https://twitter.com/vcockenpot/status/747528609502470148

Localization

 superficial lipomas (cutaneous lipoma)
 endobronchial lipoma
 soft tissue lipoma
 deep lipoma

• intramuscular lipoma
• tendon sheath lipoma
• lombosacral lipoma
• intraneural fibrolipoma and perineural fibrolipoma
• retroperitoneal lipoma

 digestive lipoma

• colorectal submucosal lipoma

Variants

 chondroid lipoma
 sclerotic lipoma
 spindle cell lipoma/pleomorphic lipoma

Cytogenetics

Conventional lipomas harbor karyotypic changes that could be subdivided into four, usually mutually exclusive, categories:
 rearrangement, in particular through translocations, of chromosome bands 12q13-15, resulting in deregulation of the HMGA2 gene
 loss of material from or rearrangement of chromosome 13
 supernumerary ring or giant marker chromosomes
 aberrations of chromosome band 6p21

83% of the cases harbor one or more of the previously known cytogenetic hallmarks.

Correlation with clinical features revealed that lipomas with rings/giant markers were larger, occurred in older patients, were more often deep-seated, and seemed to have an increased tendency to recur locally, compared with tumors with other chromosome aberrations.

Well-differentiated liposarcomas (WDLPS) classically contain high-level amplification of 12q14-15 sequences, including the MDM2 and CDK4 genes, while lipomas are characterized by simple structural chromosome aberrations often involving HMGA2 at 12q15.

Low-level gain of the 12q14-15 region, such as trisomy 12 and 12q15-24 duplication, might be sufficient for the development of minimal atypia and formation of WDLPS.

Moreover, because some features, such as overexpression of HMGA2, are shared by both lipomas and WDLPS, it has been hypothesized that lipomas and WDLPS may form a genetic and morphological continuum.

Rearrangements - translocations

More than half the cases studied show an abnormal karyotype, mostly balanced translocation, as single abnormality.

 10q22-23 rearrangement
 6p21-23 rearrangement

• target gene: HMG1A

 8q11-12 rearrangement (HMGA1, PLAG1)

 12q13-15 rearrangements

• HMGA2 rearrangement (HMGIC)
• with 3q27-28 (LPP from LIMs family)

 13q11-q22

 t(1;8)(q32;q22-q23) (1q32 and 8q23-8q23) (11943344)

Molecular biology

 sporadic lipomas

• HMGA2/RDC1 fusion protein expression in lipomas as the result of chromosome aberrations involving 2q35-37 and 12q13-15. (Fusion of RDC1 with HMGA2 in lipomas)

 predisposition to lipomas

• HMGA2: Constitutional rearrangement of HMGA2 in a phenotype including extreme somatic overgrowth, advanced endochondral bone and dental ages, a cerebellar tumor, and multiple lipomas. (15593017)

Differential diagnosis

 atypical lipomatous tumor (well-differentiated liposarcoma)

See also

 Tumors

• soft tissue tumors
  • adipose tissue tumors (adipocytic tumors)
    • benign adipose tissue tumors

Open references

 https://www.ncbi.nlm.nih.gov/books/NBK482343/

References

 Italiano A, Cardot N, Dupré F, Monticelli I, Keslair F, Piche M, Mainguené C, Coindre JM, Pedeutour F. Gains and complex rearrangements of the 12q13-15 chromosomal region in ordinary lipomas: the "missing link" between lipomas and liposarcomas? Int J Cancer. 2007 Jul 15;121(2):308-15. PMID: 17372913

 Bartuma H, Hallor KH, Panagopoulos I, Collin A, Rydholm A, Gustafson P, Bauer HC, Brosjo O, Domanski HA, Mandahl N, Mertens F. Assessment of the clinical and molecular impact of different cytogenetic subgroups in a series of 272 lipomas with abnormal karyotype. Genes Chromosomes Cancer. 2007 Jun;46(6):594-606. PMID: 17370328