pilocytic astrocytoma

Digital cases

 HPC:246 : Pilocytic astrocytoma

Definition: Juvenile pilocytic astrocytomas (JPA), a subgroup of low-grade astrocytomas (LGA), are common, heterogeneous and poorly understood subset of brain tumours in children.

Images

 https://twitter.com/chioseasi/status/715987893127356416
 https://twitter.com/KUSAURAP/status/739441710887895042

 Rosenthal fibers

• https://twitter.com/rxmsimages/status/718719835723603968

Molecular biology

 oncogenic FAM131B-BRAF fusion resulting from 7q34 deletion

• Oncogenic FAM131B-BRAF fusion resulting from 7q34 deletion comprises an alternative mechanism of MAPK pathway activation in pilocytic astrocytoma. (21424530)
• Oncogenic RAF1 rearrangement and a novel BRAF mutation as alternatives to KIAA1549:BRAF fusion in activating the MAPK pathway in pilocytic astrocytoma. (19363522)

 7q34 duplication

• Chromosomal 7q34 duplication leading to fusion genes formed between KIAA1549 and BRAF and subsequent constitutive activation of BRAF was recently identified in a proportion of LGA, and may be involved in their pathogenesis.
• Variants of JPA might arise from a unique site-restricted progenitor cell where 7q34 duplication, a hallmark of this tumour-type in association to MAPK-kinase pathway activation, potentially plays a site-specific role in their pathogenesis.
• Importantly, gain of function abnormalities in components of MAP-Kinase signalling are potentially present in all JPA making this tumour amenable to therapeutic targeting of this pathway. (19603027)

Open references

 Pilocytic astrocytoma: pathology, molecular mechanisms and markers. Collins VP, Jones DT, Giannini C. Acta Neuropathol. 2015 Jun;129(6):775-88. doi : 10.1007/s00401-015-1410-7 PMID: “25792358“ (Free)

References

 Duplication of 7q34 is specific to juvenile pilocytic astrocytomas and a hallmark of cerebellar and optic pathway tumours. Jacob K, Albrecht S, Sollier C, Faury D, Sader E, Montpetit A, Serre D, Hauser P, Garami M, Bognar L, Hanzely Z, Montes JL, Atkinson J, Farmer JP, Bouffet E, Hawkins C, Tabori U, Jabado N. Br J Cancer. 2009 Aug 18;101(4):722-33. PMID: 19603027