Expression Profiling, Oncotype DX Assay
TERMINOLOGY
Abbreviations
Quantitative reverse transcriptase polymerase chain reaction (QRT-PCR)
21 gene RT-PCR breast cancer gene profiling assay (Oncotype Dx [Genomic Health; Redwood City, CA])
Recurrence score (RS)
National Surgical Adjuvant Breast and Bowel Project (NSABP)
Types of Tests
Gene expression profiling studies of breast cancer have demonstrated potential clinical applications
Provide clinically relevant biologic classification of breast cancer patients
Assessment of prognosis and potential for recurrence that is significant and independent of other pathologic factors
Help predict response to adjuvant and neoadjuvant therapies
Endocrine therapy
Chemotherapy
Targeted therapies
Significant technical limitations of expression profiling studies for clinical samples in routine practice
Current technology requires fresh or snap frozen tissue, which contain high quality RNA that has not degraded
Limited dynamic range for gene assays, difficult to control
Alternative approach to molecular profiling of breast cancer
Application of QRT-PCR to formalin-fixed paraffin-embedded clinical samples
Used to quantify expression of potentially clinically important, tumor-related gene transcripts in multigene approach
QRT-PCR assay for genes utilizes forward primer, reverse primer, and probe
Probes and primers are specific sequences that are complementary and bind to specific RNA transcript to be assayed
Ends of gene probe are capped with fluorescence label on 1 end and fluorescence quencher on other
Used to measure amount of RNA present and level of gene expression
During PCR, DNA polymerase displaces and cleaves probe, releasing fluorescent label
Rate of rise of fluorescence as label is released depends on amount of starting RNA present
Rate of rise of fluorescence can be used to quantitatively measure level of gene expression
QRT-PCR has wide dynamic range
High sensitivity and specificity for results
Results are highly reproducible
Definitions
Validated 21-gene RT-PCR assay (Oncotype Dx) was developed for use in routine paraffin-embedded breast cancer samples
Developed through collaborations between Genomic Health Incorporated (Redwood City, CA) and NSABP
Helps predict likelihood of recurrence and the magnitude of benefit from adjuvant chemotherapy
Oncotype Dx assay utilizes TaqMan® (Invitrogen; Carlsbad, CA) quantitative PCR
Measures quantitatively a selected panel of 21 gene transcripts
16 cancer-related genes and 5 reference genes
Algorithm based on level of gene expression used to calculate recurrence score
Assay validated for patients with ER positive, node-negative breast cancers treated with tamoxifen
Reference genes are used to normalize level of expression of cancer-related genes
Helps to control for RNA fragmentation, which occurs in formalin-fixed tissue
Target Gene or Antigen
16 cancer-related genes are used to calculate RS
Selected genes weigh most heavily tumor proliferation, hormone receptor status, and HER2 expression
Used to help predict likelihood of disease recurrence at 10 years
Calculated RS in ER(+) node(-) breast cancer ranges from 0-100
Divides patents into 3 categories in terms of their 10-year distant recurrence-free survival
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
