Cancer and Genetics I

Question 1

describe hemochromatosis and genetic testing for it

Answer 1

PCR –> restriction endonucleases on the HFE gene

• hemochromatosis (type I) –> mutation in HFE gene
  
  • C282Y = 90%, H63D = 1%
• defective function of this gene leads to excessive iron absorption and deposition
• chronic fatigue, arthritis, heart disease, cirrhosis, diabetes
• frequency = 1/200 in North America
• other types:
  
  • type 2a: hemojuvelin mutation
  • type 2b: hepcidin mutation
  • type 3: transferrin receptor 2 mutation

Question 2

describe Factor V Leiden

Answer 2

• mutation changes factor V protein making it resistant to inactivation by protein C – thrombophilia and venous thromboembolism
• heterozygous and homozygous mutation increases risk of thromboembolism, further aggravated by oral contraceptive, pregnancy, surgery

Question 3

describe genetic testing for Factor V Leiden

Answer 3

PCR –> restriction endonucleases

Question 4

describe tumor susceptibility based on gene mutations

Answer 4

• BRCA1/2: breast and ovarian cancer
• RET: MEN syndrome
• P53: Li Fraumeni syndrome
• APC: adenomatous polyposis

Question 5

HNPCC is characterized by…

Answer 5

• younger age at diagnosis
• synchronous and metachronous tumors in the right colon
• also tumors in endometrium, ovary, stomach, small bowel, ureter and kidney
• HNPCC related tumors in 1st degree relative

Question 6

describe microsatellite instability (MSI)

Answer 6

defects in Lynch syndrome (HNPCC)

• microsatellite
  
  • short repetitive DNA segments in non-coding region
• MSI = change in length of microsatellite due to insertion/deletion
• failure of error correction by mismatch repair (MMR) system during DNA replication –> MSI

Question 7

describe testing for HNPCC

Answer 7

• protein level: immunocytochemistry in the tissues using antibody
• if the genes are mutated or methylated, their protein products will be absent in the tumor

Question 8

describe testing for microsatellite instability (MSI)

Answer 8

• confirmation by sequencing
• however before sequencing:
  
  • testing for BRAF V600E gene mutation is done
  • BRAF V600E mutation is NOT present in patients with germline mutation and is associated with promoter methylation of MLH1

Question 9

describe gene rearrangement testing

Answer 9

• paraffin embedded tissues were subjected to DNA extraction and IGH gene rearrangement tests
  
  • the products are analyzed on polyacrylamide gel
• monoclonal type of IGH gene rearrangement

Question 10

describe tests for prediction of malignancies

Answer 10

BRCA1/BRCA2

Question 11

describe tests for prognosis of malignancy

Answer 11

NMYC, HER2/NEU, LOH, MSI

Question 12

describe tests for diagnosis of metastasis/tumor characterization

Answer 12

specific mRNA detection: PSA, tyrosinase, cytokeratin

Question 13

describe synovial sarcoma and genetic testing for it

Answer 13

RNA extracted from tissue, RT-PCR for the mRNA was performed (RNA –> DNA first via RT)

• tumors of adolescents and young adults
• 2 histologic types:
  
  • biphasic: epithelial and mesenchymal cells
  • monophasic: predominantly spindle cells
• t(X:18)

Question 14

describe HER2 (neu) and genetic testing for it

Answer 14

• 25% breast cancer: amplification of the human epidermal growth factor receptor 2 (HER2) gene
• HER2 overexpression correlates with:
  
  • aggressive features
  • shortened disease-free survival
• Herceptin (antibody against Her2 protein) treatment

Question 15

describe K-RAS (and genetic testing) and anti-EGFR treatment

Answer 15

detection: sequencing, scorpion reaction (PCR variation)

Question 16

describe BRAF in melanoma and how to test for it

Answer 16

• 40-60% of melanomas contains BRAF mutation >> MAP kinase activation
• majority results in substitution of glutamic acid for valine at amino acid 600 (V600E)
• mutation = aggressive behavior
• test by RT-PCR/sequencing
• targeted therapy

Question 17

describe treatment of non-small cell lung cancer (NSCLC)

Answer 17

• mutations in EGFR, KRAS and anaplastic lymphoma kinase (ALK) are mutually exclusive
• EGFR tyrosine kinase inhibitors (TKIs) are effective in tumors with:
  
  • mutations within the EGFR
  • RAS mutations are resistant to TKI
• patients with ALK mutation are not treated by EGFR-targeting TKIs but with ALK inhibitor instead

Question 18

describe the treatment breakdown of NSCLC

Answer 18

Question 19

describe testing for CML

Answer 19

cytogenetic analyses done by double fusion FISH (D-FISH)

testing may also be performed by RT-PCR

Question 20

describe CML and a potential treatment for it

Answer 20

• incidence of CML is 1-2 per 100,000
• CML caused by t(9,22)
• the product of this fusion gene is BCR-ABL tyrosine kinase
• Gleevec is an inhibitor of BCR-ABL kinase
  
  • an effective therapy for CML
• Gleevec is also used in the treatment of GI stromal tumors

Question 21

describe transplantation testing

Answer 21

• tissue antigen matching
• engraftment
  
  • similar tests as identity testing
  • X chromosome probes

Question 22

describe diagnosis and treatment of acute lymphoblastic leukemia (ALL)

Answer 22

• TPMT - SNP analysis was performed before maintenance on oral mercaptopurine
  
  • a SNP in TPMT leads to increased blood levels of 6-mercaptopurine and toxicity, therefore need to administer lower dose

Question 23

____ are major factors influencing drug response

Answer 23

SNPs are major factors influencing drug response