The Recurrence Score (RS) of Oncotype DX™ is an independent predictor of the risk of distant recurrences among node-negative and node-positive, hormone-positive early breast cancer patients who are treated with either tamoxifen (Nolvadex®) or Arimidex® (anastrozole). These results were recently presented at the 2008 San Antonio Breast Cancer Symposium.

Oncotype DX®, the reverse transcription polymerase chain reaction (RT-PCR) 21-gene assay, represents a major milestone in the progress of individualized therapy. Oncotype DX is a clinically validated test that quantitatively predicts the likelihood of breast cancer recurrence in women with newly diagnosed, early-stage invasive breast cancer and assesses the benefit these patients will achieve from chemotherapy. Oncotype DX has been included in the NCCN and ASCO guidelines for patients with estrogen-receptor positive early breast cancer to help guide treatment decisions. The 21-gene assay stratifies patients according to their risk of a recurrence by a Recurrence Score (RS). Patients with a score less than 18 have a low risk of recurrence, those with an RS score between 18-30 have an intermediate risk of recurrence, and those with a score greater than 30 have a high risk of recurrence. Oncotype DX has also demonstrated the ability to determine ER/PR and HER status, results that are now included as part of the assay’s results.

More recently, researchers evaluated ability of Oncotype DX to predict the risk of distant recurrences among postmenopausal women with hormone-positive breast cancers who are treated with Arimidex. The recent trial included 1,308 hormone receptor-positive tumor blocks that were collected retrospectively from patients in the monotherapy arms of the ATAC (Arimidex, tamoxifen, or both trial), in which postmenopausal patients with early breast cancer were treated with either Arimidex or tamoxifen as monotherapy or with sequential administration of both agents. The primary analysis was the relationship between the rate of distant recurrences and the RS of Oncotype DX.

• At nine years distant recurrence-free rates among lymph node-negative patients were 96% for patients with a low RS, 88% for those with an intermediate RS, and 75% for patients with a high RS (P<0.001).
• At nine years distant recurrence-free rates among lymph node-positive patients were 83% for patients with a low RS, 72% for those with an intermediate RS, and 51% for those with a high RS (P<0.001).
• Tumor size was also an independent predictor of time to distant recurrence.
• The adjusted hazard ratio of the RS as a variable in determining risk of a distant recurrence was 5.25 (2.84-9.73); P<0.001.

The researchers concluded that Oncotype DX is an independent predictor of the risk of recurrence among postmenopausal patients with early, hormone-positive breast cancer who are treated with Arimidex.

Reference: Dowsett M, Cuzick J, Wales C, et al. Risk of distant recurrence using Oncotype DX in postmenopausal primary breast cancer patients treated with anastrozole or tamoxifen: a TransATAC study. Program and abstracts of the 31st Annual San Antonio Breast Cancer Symposium; December 10-14, 2008; San Antonio, Texas. Abstract 53.