Genomic Assays

Genomic Assays:  Oncotype DX and MammaPrint

Genomic assays are a relatively new type of test that analyzes the breast tumor for the activity of a group of genes that can help predict the risk of whether that breast cancer will recur either locally or distant.  They provide important information on the value of chemotherapy, preventing unnecessary side effects in patient who have a low likelihood of recurrence or response to chemotherapy.  Two such tests are currently in use, Oncotype DX (which investigates 21 genes) and MammaPrint (which considers 70 genes), with others under development.  These tests are generally used only for patients who have early-stage breast cancer, that has not invaded the lymph nodes, or for hormone-receptor positive patients, who can be treated with hormone therapy.  They help patients (and their doctors) make the often difficult choice of whether to undergo chemotherapy.  By providing a genetic profile, these tests predict the risk of recurrence and the possible benefit of chemotherapy.

The Oncotype DX test, is used only on node-negative and hormone receptor-positive tumors.  It divides patients in to a low-risk, intermediate-risk, and high-risk group based on the recurrence score calculated.  A score lower than 18 means that the risk of recurrence is low and the benefit of chemotherapy is small, and typically not recommended.   A score of 18-30 indicates an intermediate risk of recurrence.  The benefits of chemotherapy, when weighed against the potential side effects, are not clear in this instance and other factors must be considered.  A score greater than 30 indicates a high risk of recurrence and chemotherapy is advised.

MammaPrint can be used on either hormone receptor-positive or negative patients with negative nodes.  This  score is reported as either low- or high-risk.  Low-risk means that the cancer has a 10% chance of recurring within 10 years without additional treatment.  High risk means that the cancer has at least a 29% risk of recurring within 10 years without additional treatment.

These tests are proving to be an important tool to help patients and their doctors make the decision whether to have additional treatment.  Genomic tests can be performed initially or subsequently, once a patient is known to be a candidate for a test.