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Breast Cancer

Review of the Clinical Studies Using the 21-Gene Assay

Division of Medical Oncology, Sunnybrook Odette Cancer Centre, The University of Toronto, Toronto, Ontario, Canada

Key Words. Recurrence score • Prognostic test • Breast cancer • Adjuvant chemotherapy

Correspondence: Kathleen I. Pritchard, M.D., F.R.C.P.C., Division of Medical Oncology, Sunnybrook Odette Cancer Centre, The University of Toronto, 2057 Bayview Avenue, Toronto, Ontario, Canada, M4N 3M5. Telephone: 416-480-4616; Fax: 416-480-6002; e-mail: Kathy.pritchard{at}sunnybrook.ca

Received November 9, 2009; accepted for publication February 10, 2010; first published online in THE ONCOLOGIST Express on April 26, 2010.

Disclosures: Catherine M. Kelly: None; Ellen Warner: None; Daphne T. Tsoi: None; Sunil Verma: None; Kathleen I. Pritchard: Consultant/advisory role: Pfizer, AstraZeneca, Roche, Novartis; Honoraria: Pfizer, AstraZeneca, Roche, Novartis.

The content of this article has been reviewed by independent peer reviewers to ensure that it is balanced, objective, and free from commercial bias. No financial relationships relevant to the content of this article have been disclosed by the independent peer reviewers.

Purpose. A major challenge in treating early-stage hormone receptor (HR)⁺ breast cancer is selecting women who, after initial surgery, do not require chemotherapy. Better prognostic and predictive tests are needed. The 21-gene assay is the only widely commercially available gene signature that can be performed on formalin-fixed paraffin-embedded tissue.

Methods. We conducted a review of the literature supporting the prognostic and predictive ability of the 21-gene assay in HR⁺ node-negative and node-positive breast cancer patients in chemotherapy-/endocrine-treated and untreated populations.

We considered: (a) How accurate is the recurrence score (RS) as a prognostic factor for distant recurrence? (b) How accurate is the RS as a predictive factor for benefit from systemic therapy? (c) How does the RS compare with other prognostic/predictive factors such as tumor size, tumor grade, patient age, and integrated decision aids such as Adjuvant! Online? (d) How do patients and physicians view the 21-gene assay? (e) What are the cost implications of the 21-gene assay?

Results. The 21-gene assay: (a) provided accurate risk information; (b) predicted response to cyclophosphamide, methotrexate, and 5-fluorouracil and to cyclophosphamide, doxorubicin, and 5-fluorouracil chemotherapy; (c) added additional information to traditional biomarkers; (d) was viewed positively by both physicians and patients; and (e) fell within the cost-effectiveness values in North America.

Conclusion. This assay may be offered to patients with node-negative HR⁺ breast cancer to assist in adjuvant treatment decisions. Data are accumulating to support the use of the 21-gene assay in HR⁺ node-positive patients.

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