TUMOR GENOMICS SLOWLY REPLACING STAGE IN DETERMINING BREAST CANCER PROGNOSIS AND TREATMENT

It was no more than a decade ago when breast cancer prognosis and treatment were determined almost exclusively by tumor size, lymph node status, and how aggressive a tumor appeared under the microscope. Tumor size and lymph node status determined stage, whereas the microscopic appearance of the cancer determined the grade. Flash forward to today, and we find an entirely new approach is evolving. Testing for genes active in cancer (called tumor genomics) is not the same as gene testing for hereditary breast cancer (germline testing). In germline testing, a patient’s blood or saliva is tested for genetic mutations that determine a woman’s risk of developing breast or other types of cancer. Tumor genomics is carried out not on blood or saliva but on the patient’s breast cancer.

Tumor genomics is performed either on the core needle biopsy tissue used for diagnosis or on the cancerous tissue removed at the time of surgery. It is essential to know that these genomic tumor tests are performed only on cancers that are positive for the estrogen receptor (ER+). Several proprietary tests are in common usage in the United States. By far, the most used test is called Oncotype Dx. Oncotype Dx generates a score which is termed a recurrence score (RS). The lower the RS, the better the prognosis and the lower the risk of recurrence.

Most importantly, patients with a low RS usually do not benefit from chemotherapy, generally requiring only hormonal therapy. The other tests in common usage are the MammaPrint and EPClin. Though an overwhelming majority of oncologists prefer Oncotype Dx, scientific data does not support using one over the other. The importance of tumor genomic testing cannot be overstated. Since its acceptance by the medical community a decade ago, the number of women required to receive postoperative chemotherapy has dropped dramatically, with no reduction in the cancer cure rate.

As previously stated, currently, tumor genomics is performed only on breast cancer that is ER+. The other biologic types of breast cancer include triple-negative (ER-, PR-, Her2-) and Her2+ cancers. Except for the very smallest of these tumors, triple-negative cancers all routinely receive chemotherapy before or after surgery. Her2 is a gene identified in about 20% of breast cancers. Though most are ER-, some are ER+. Patients with this type of cancer also routinely receive pre or postoperative chemotherapy and a biologic drug directly targeting the gene. It is likely, looking ahead, that tumor genomics will gain importance even in triple-negative and Her2+ tumors.