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Hereditary Breast Cancer: Case Study Essay Example

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Published: January 9, 2018

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Sporadic Cancers

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-develop with no obvious inheritance pattern -majority of causes of malignancies

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Inherited Cancers

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-inherit an increased susceptibility to develop cancer at some times in their lives -events after birth will trigger the cancer development -cancers in this group can also sometimes be sporadic

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Oncogenes

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-class of genes who presence initiates the development of cancer by excessive cellular proliferation -arise from normal cellular genes: porto-oncogenes: essential for the regulation of cell proliferation and survival -oncogenes represent altered gene structure which affects expression

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Examples of oncogenes: RAS

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-point mutation: AA substitution

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-RAS: rat sarcoma -Bladder, lung, colon, pancreas

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Examples of oncogenes: gene amplification

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-creation of multiple duplicate copies of same gene -Myc: avian myelocytomatosis -excessive amounts of myc which control cell proliferation -breast, ovary, pancreas, lung, esophagus

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Examples of oncogenes: chromosomal translocation

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-portion of one chromosome is transferred to another chromosome -Abnormal version of chromosome 22 (philadelphia chromosome) -CML: breakage has occurred near ends of 9 and 22 and are translocated--> over expressed fusion protein -t9:22-bcr-abl

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Examples of oncogenes: localized DNA rearrangements

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-deletions, insertions, transpositions, inversions -fusions genes and fusion proteins that stimulate cell activity -TRK (tyrosine kinase) oncogene: growth factor which permanently activates a tyrosine kinase side *hereditary colon cancer*

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Examples of oncogenes: Insertional mutagensis

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-Viral conversion of gene into oncogene -some viruses, possessing no oncogenes, if inserted next to a porto-oncogene may trigger overproduction of normally produced protein -Avain Leukosis Virus: possesses long terminal repeats (LTR) -if inserted next to the MYC can trigger overproduction *EBV, HCV, HBV, HPV, HTLV-1, KSHV

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Gain of function mutations

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-protein products exhibit new or excessive activity *multiple endocrine neoplasia II* (Men II) -bening and malignant tumors of endocrine glands -inheritance of single *RET gene* (receptor tyrosine kinase)

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Loss of Function: Rb gene

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-ABSENCE of the Rb gene results in hereditary retinoblastoma -Rb usually halts cell cycle at restriction point, when mutated cells grow unhindered

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Loss of Function: P53 gene

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-most common tumor suppressor gene is P53 -mutated in half of all cancer cases -P53 normally gets phosphorylated when cells undergo DNA damage--> accumulation of phosphorylated P53 induces cell cycle arrest and destruction When mutated: damaged cells can proliferate

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BRCA1 and BRCA2

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-proteins produced by these genes are involved in repairing damaged DNA -BRCA1 and BRCA2 mutations seen in hereditary, not so much in sporadic cancers -do not control cell proliferation, and are only indirectly related to cancer development -unlike Rb and P53 -cells deficient in either one of the brA proteins exhibit large numbers of chromosomal abnormalities--> they usually repair double strand breaks -count for 3% of all breast cancers -hundred of

mutations identified in each gene, some risker than others -higher risk of other epithelial cancers: prostate, pancreas

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Repair of double strand Breaks

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1) Non-homologous end joining: ~if BRCA genes are mutated, this is the mechanism the cell uses ~very prone to mistakes--> increased risk of carcinogenic agents 2) homologous recombination: ~less prone to error because it uses DNA in unbroken homologous chromosome to serve as template for repair ~involves BRCA's *pathway activated by ATM Kinase: phosphorylates and activates more than a dozen proteins in cell control and DNA repair

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BRCA1

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-located on chromosome 17q21 -ER-, Her2- -increased risk of ovarian carcinoma: 20-40% of carriers

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BRCA2

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-located on 13q12.3 -ER+, Her2- -Increased risk of ovarian cancer in 10-20% -more frequent in male breast cancers

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Penetrance

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-Penetrance is the % of carriers who develop the cancer -BRCA 1 and BRCA 2 penetrance can be 30-90% -lifetime breast cancer risk in women with these mutations as *high as 85%* -median age at diagnosis is 20 years earlier than women without

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Probability of breast cancer associated with a mutation in one of these genes increases with:

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1) there are multiple affected first degree relatives 2) individuals are affected before menopause and/or have other cancers 3) there is a case of male breast cancer in one of the first degree relatives 4) one of the first degree family members also

develops ovarian cancer

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