Stage II colon cancer patients have a tough time knowing how likely it is that their cancer will recur and making a decision about having chemotherapy after surgery.
A test is now on the market that can help with that decision. OncoType DX® Colon Assay analyzes 12 key genes from a tumor sample to produce a recurrence score that indicates how likely stage II colon cancer will return.
While OncoType DX Colon can’t predict whether chemotherapy will reduce the chance that cancer will come back, it can help patients and their doctors decide on chemotherapy in combination with other factors.
Based on many years of studying tumor samples saved in paraffin during clinical trials, OncoType DX analyzes expression of 12 genes in colon tumors. The resulting recurrence score determines the likelihood that cancer will recur in the following three years.
At ASCO in 2009, development and validation of the 12 gene test was announced, and Genomic Health predicted a commercial launch of the test in early 2010.
Range of recurrence scores:
- Low — About 44 percent of patients will have about a 12 percent risk of recurrence.
- Intermediate — About 31 percent will have an 18 percent risk of recurrence.
- High — 26 percent will have a 22 percent risk
Genomic Health scientists recommend that the actual recurrence core itself be considered, rather than a general low, intermediate, or high.
Two other factors that are important in deciding whether or not to use chemotherapy are
- Mismatch repair status: In about 15 percent of stage II colon cancer, genes that help repair damaged DNA are mutated. Mismatch repair is deficient (dMMR). Patients with these tumors have good survival prospects and are much less likely to experience recurrence. Studies show that chemotherapy doesn’t reduce recurrence or improve survival, and some studies show reduced benefit with chemo, although this remains controversial. Most tumors, however, are have not lost the ability to repair DNA and are labeled MMR proficient (pMMR).
- T-stage: Stage II colon cancer is either T3 or T4. In T3 colon cancer, the tumor has grown outer muscular layer of the colon and into the outermost layers not through them. It has not reached any nearby organs or tissues. A cancer that has broken through the wall of the colon and may be in nearby tissues is classified as T4. T4 cancers have almost double the risk of recurrence.
Most oncologists would agree that risk is high for T4 tumors with proficient mismatch repair and chemotherapy is probably warranted after surgery. For T3 tumors that have deficient mismatch repair, chemotherapy probably has no benefit and may even be detrimental.
But three out of four stage II colon cancers fall into an intermediate risk category of T3 stage and proficient mismatch repair. For patients with these tumors, the OncoType DX recurrence score can be valuable in helping make a decision about further treatment.
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