Oncotype DX Colon Cancer Assay
The Oncotype DX Colon Cancer Assay, developed by Genomic Health, is a genomic test that has been clinically available for patients with newly diagnosed stage II colon cancer, since January 2010. The test is a validated diagnostic assay based on an individual patient’s colon tumor expression of 12 genes, which quantifies the likelihood of recurrence in stage II colon cancer following surgery. The result from the assay is a continuous Recurrence Score® value from 0 to 100 that corresponds to a specific likelihood of colon cancer recurrence 3 years after surgery. A lower score corresponds to a lower risk of recurrence, and a higher score corresponds to a higher risk of recurrence. The Recurrence Score result provides additional information on recurrence risk beyond traditional clinical and pathological characteristics such as tumor stage (T-stage), mismatch repair (MMR) status, number of lymph nodes examined, tumor grade and lymphovascular invasion . The Oncotype DX Colon Cancer Assay has the greatest utility for the stage II colon cancer patients with T3 and MMR proficient tumors.
The Oncotype DX assay is a non-invasive test that is performed on a small amount of the tissue removed during surgery, which means no additional invasive procedure is required. After the surgical procedure, the tissue sample is fixed (usually in formalin) and embedded in paraffin so it can be preserved for diagnostic testing. To perform Oncotype DX test, a pathologist will send the tumor block or several thin sections of the tissue sample to Genomic Health. Genomic Health uses a laboratory process known as RT-PCR to measure the expression of the 12-gene panel.
Prior to selecting genes for the Oncotype DX Colon Cancer Assay, feasibility studies were conducted to optimize the Genomic Health platform for quantitative assessment of gene expression from fixed paraffin-embedded (FPE) colon tumor tissue. These studies in FPE colon tumor tissue identified (1) the optimal method for reliably extracting RNA and measuring gene expression by quantitative RT-PCR technology, (2) the requirement for review of each case by a pathologist for manual microdissection to remove normal colon tissue adjacent to the tumor, and (3) reference genes for normalization of gene expression. The use of carefully selected reference genes to normalize gene expression in the context of sources of pre-analytical variability such as time of fixation and block age is a critical feature of this technology. The findings from these feasibility studies provided the technical foundation for subsequent studies.
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