RATIONALE: Studying samples of tumor tissue from patients with cancer in the laboratory may help doctors identify and learn more about biomarkers related to cancer. It may also help doctors predict whether cancer will come back after treatment.

PURPOSE: This research trial is studying genes that may predict local recurrence in samples from patients with breast cancer. treated on NSABP-B-28

OBJECTIVES:

• To evaluate the association between the 21-gene Recurrence Score and risk of local-regional recurrence (LRR) in node-positive, estrogen receptor- (ER) positive (+) patients treated with cyclophosphamide and doxorubicin hydrochloride (AC) with or without paclitaxel in the NSABP-B-28 trial.
• To evaluate the potential for combining the 21-gene Recurrence Score (RS) with traditional clinico-pathologic factors in order to derive an improved algorithm for prediction of LRR risk and in order to identify subgroups of ER-positive patients with 1-3 or 4 or more positive nodes who do/do not need post mastectomy chest wall radiotherapy (XRT) or regional nodal XRT (irrespective of surgical procedure).
• To evaluate whether the 21-gene RS predicts benefit from adding paclitaxel to AC chemotherapy in reducing risk of LRR, and improving disease-free survival (DFS) and overall survival (OS) in node-positive, ER-positive patients from NSABP-B-28.

OUTLINE: RNA extracted from paraffin-embedded tissue samples are analyzed for gene expression profile by Ribogreen assay and RT-PCR. Results are then compared and analyzed with each patient clinical-pathologic factors, including tumor size, patient age, number of positive nodes (1-3, 4+), tumor grade, and surgery type (mastectomy or lumpectomy).

DISEASE CHARACTERISTICS:

• Diagnosed with breast cancer and enrolled on NSABP-B-28.

  • Estrogen-receptor positive (ER+)
  • Node-positive disease

• Primary tumor tissue samples available

• Treated with cyclophosphamide and doxorubicin hydrochloride and tamoxifen with or without paclitaxel

PATIENT CHARACTERISTICS:

• Menopausal status not specified

PRIOR CONCURRENT THERAPY:

• See Disease Characteristics

Stored tissue from participants in protocol NSABP B-28.