Retinoblastoma pathophysiology
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [2]Associate Editor(s)-in-Chief: Simrat Sarai, M.D. [3]
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Overview
On gross pathology, viable tumor cells near blood vessels and zones of necrosis in avascular areas are characteristic findings of retinoblastoma. On microscopic histopathological analysis, small, round-cell tumor of neuroepithelial origin, Flexner-Wintersteiner rosettes, and Homer-Wright rosettes are characteristic findings of retinoblastoma. Retinoblastoma can be bilateral or unilateral, spontaneous or familial. In 30% to 40% of cases, retinoblastoma is accompanied by a germinal mutation in the RB1 gene.[1]
Pathogenesis
- Retinoblastoma is a neoplasm which is caused by the inactivation of RB1 gene, a tumor suppressor gene.[2]
- Normally, RB1 gene is necessary for the normal differentiation and growth of retinal stem cells and its mutation results in unregulated growth of these cells and development of the tumor.
- Mutation in both alleles of the RB1 gene is necessary for the inactivation of the gene.[3]
- This disorder may occur in the familial or sporadic form.
- In the familial form (48% of the cases), the first mutation occurs during germ cell division and the second one later during the division of somatic cells.[4]
- In the sporadic form, both mutations occur during the lifetime of the individual.
Genetics
- Retinoblastoma occurs due to mutational inactivation of RB1 gene located on the chromosome 13.[5]
- Two mutational events are needed for the development of retinoblastoma.
- In familial form, with autosomal dominant inheritance, one mutation occurs in the germline and the second one during the somatic division of the retinal cells.
- In the acquired form, both mutations occur during somatic divisions.
- Another gene which has been associated with the pathogenesis of retinoblastoma is MYCN gene.[6]
- Somatic amplification of MYCN oncogene is responsible for <3% of the non-heritable form of the retinoblastoma cases.
Usually retinoblastoma is caused by mutational inactivation of both alleles of the retinoblastoma (RB1) gene.[7] The RB1 gene maps to chromosome 13q14 and encodes a nuclear protein (Rb) that acts as a tumor suppressor.[8][9][10] This protein (Rb) restricts the cell's ability to progress from the G1 phase to the S phase of the cell cycle.[11] Rb binds to E2F, a transcription factor, when active. Loss of this active, functional protein (Rb) causes cell cycle dysregulation. The inherited form of retinoblastoma is due to a germline mutation that can be either familial or sporadic.[12] Retinoblastoma may be unilateral or bilateral.
- Bilateral tumors (30-40% of cases) essentially always have a germline mutation. In 10 percent of bilateral patients, a positive history of retinoblastoma is seen, which suggests that the majority of bilateral cases arise from a new germline mutation.
- Unilateral tumors (60-70% of cases) are caused by a germline mutation in approximately 15% of cases, whereas 85% are sporadic. Patients with unilateral disease can also have the heritable form of the disease; these are often multifocal and account for 12 to 15 percent of retinoblastoma cases. The remaining children with retinoblastoma have the unilateral, non-germline, and non-heritable form of the disease.
- Thus, approximately 30% to 40% of cases are due to a germline mutation. This mutation is inherited in an autosomal dominant fashion with approximately 90% penetrance (i.e the child of a retinoblastoma survivor who has a germline mutation has a 50% chance of inheriting a mutation, and if they do so a 90% chance of developing retinoblastoma. Thus there is an overall chance of 45% of having retinoblastoma (50% x 90%).[13]
Gross Pathology
- Macroscopic appearance of the tumor varies according to the staging of the tumor.[14]
- The tumor is white and has areas of calcification and necrosis.
- The presence of calcium is more noticeable when the tumor was treated via prior chemotherapy or radiotherapy.
Macroscopically, viable tumor cells are found near blood vessels, while zones of necrosis are found in relatively avascular areas. Macroscopic examination reveals a white elevated mass with fine surface vessels. Early retinoblastoma presents as a solitary or multifocal, well-circumscribed translucent mass. The tumor becomes more pink in color, with dilated feeding blood vessels as the disease advances. The tumor may exhibit three patterns of growth, which is tabulated below:
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Microscopic Pathology
Microscopically, retinoblastoma is a neoplasm consists of:[16]
- Small hyperchromatic cells with a high nuclear to cytoplasmic ratio
- Large areas of necrosis
- Multifocal area of calcifications
Microscopically, both undifferentiated and differentiated elements may be present.[17]
- Undifferentiated elements appear as collections of small, round cells with hyperchromatic nuclei
- Differentiated elements include:
- Flexner-Wintersteiner rosettes
- Homer-Wright rosettes
- Fluerettes from photoreceptor differentiation
![Retinoblastoma 400 X magnification[18]](/index.php/File:Retinoblastoma_Pathology_(2).jpg)
![Flexner- Wintersteiner Rosettes in retinoblastoma[18]](/index.php/File:Flexner-_Wintersteiner_Rosettes_in_Retinoblastoma.jpg)
References
- ↑ Schefler AC, Abramson DH (2008). "Retinoblastoma: what is new in 2007-2008". Curr Opin Ophthalmol. 19 (6): 526–34. doi:10.1097/ICU.0b013e328312975b. PMID 18854698.
- ↑ Dunn JM, Phillips RA, Becker AJ, Gallie BL (September 1988). "Identification of germline and somatic mutations affecting the retinoblastoma gene". Science. 241 (4874): 1797–800. PMID 3175621.
- ↑ Dunn JM, Phillips RA, Zhu X, Becker A, Gallie BL (November 1989). "Mutations in the RB1 gene and their effects on transcription". Mol. Cell. Biol. 9 (11): 4596–604. PMC 363605. PMID 2601691.
- ↑ Garber JE, Offit K (January 2005). "Hereditary cancer predisposition syndromes". J. Clin. Oncol. 23 (2): 276–92. doi:10.1200/JCO.2005.10.042. PMID 15637391.
- ↑ Knudson AG (April 1971). "Mutation and cancer: statistical study of retinoblastoma". Proc. Natl. Acad. Sci. U.S.A. 68 (4): 820–3. PMC 389051. PMID 5279523.
- ↑ Fabian ID, Rosser E, Sagoo MS (2018). "Epidemiological and genetic considerations in retinoblastoma". Community Eye Health. 31 (101): 29–30. PMC 5998388. PMID 29915469.
- ↑ Finger, Paul T; Harbour, J.William; Karcioglu, Zeynel A (2002). "Risk Factors for Metastasis in Retinoblastoma". Survey of Ophthalmology. 47 (1): 1–16. doi:10.1016/S0039-6257(01)00279-X. ISSN 0039-6257.
- ↑ Friend, Stephen H.; Bernards, Rene; Rogelj, Snezna; Weinberg, Robert A.; Rapaport, Joyce M.; Albert, Daniel M.; Dryja, Thaddeus P. (1986). "A human DNA segment with properties of the gene that predisposes to retinoblastoma and osteosarcoma". Nature. 323 (6089): 643–646. doi:10.1038/323643a0. ISSN 0028-0836.
- ↑ Fung, Y.; Murphree, A.; T'Ang, A; Qian, J; Hinrichs, S.; Benedict, W. (1987). "Structural evidence for the authenticity of the human retinoblastoma gene". Science. 236 (4809): 1657–1661. doi:10.1126/science.2885916. ISSN 0036-8075.
- ↑ Lee, W.; Bookstein, R.; Hong, F.; Young, L.; Shew, J.; Lee, E. (1987). "Human retinoblastoma susceptibility gene: cloning, identification, and sequence". Science. 235 (4794): 1394–1399. doi:10.1126/science.3823889. ISSN 0036-8075.
- ↑ Goodrich, David W.; Wang, Nan Ping; Qian, Yue-Wei; Lee, Eva Y.-H.P.; Lee, Wen-Hwa (1991). "The retinoblastoma gene product regulates progression through the G1 phase of the cell cycle". Cell. 67 (2): 293–302. doi:10.1016/0092-8674(91)90181-W. ISSN 0092-8674.
- ↑ Leiderman, Yannek I.; Kiss, Szilárd; Mukai, Shizuo (2007). "Molecular Genetics ofRB1——The Retinoblastoma Gene". Seminars in Ophthalmology. 22 (4): 247–254. doi:10.1080/08820530701745165. ISSN 0882-0538.
- ↑ Retinoblastoma. Radiopedia(2015) http://radiopaedia.org/articles/retinoblastoma Accessed on October 10, 2015
- ↑ Das D, Bhattacharjee K, Barthakur SS, Tahiliani PS, Deka P, Bhattacharjee H, Deka A, Paul R (May 2014). "A new rosette in retinoblastoma". Indian J Ophthalmol. 62 (5): 638–41. doi:10.4103/0301-4738.129786. PMC 4065523. PMID 24881618.
- ↑ Image courtesy of Dr. Frank Gaillard Radiopaedia (original file [1]).[http://radiopaedia.org/licence Creative Commons BY-SA-NC
- ↑ Kashyap S, Sethi S, Meel R, Pushker N, Sen S, Bajaj MS, Chandra M, Ghose S (February 2012). "A histopathologic analysis of eyes primarily enucleated for advanced intraocular retinoblastoma from a developing country". Arch. Pathol. Lab. Med. 136 (2): 190–3. doi:10.5858/arpa.2010-0759-OA. PMID 22288967.
- ↑ Retinoblastoma. Wikipedia(2015) https://en.wikipedia.org/wiki/Retinoblastoma Accessed on October 10 2015
- ↑ 18.0 18.1 Images of microscopic appearance of retinoblastoma. Wikipedia 2015. https://en.wikipedia.org/wiki/Retinoblastoma