PROGNOSTIC-SIGNIFICANCE OF S-PHASE FRACTION IN GOOD-RISK, NODE-NEGATIVE BREAST-CANCER PATIENTS

Purpose: Formalin-fixed, paraffin-embedded tissues from axillary node- negative breast cancer patients were analyzed by flow cytometry to determine the prognostic significance of DNA ploidy and S-phase fraction (SPF). Patients and Methods: All patients were registered on a good-risk control arm of an intergroup clinical trial. They had small- to intermediate-sized (< 3 cm), estrogen receptor (ER)-positive tumors and received no adjuvant therapy after modified radical mastectomy or total mastectomy with low axillary-node sampling. The median follow-up was 4.8 years. Results: Assessable ploidy results were obtained from 92% of the 298 specimens studied (51% diploid, 49% aneuploid), and SPFs were assessable for 83% of the tumors. SPFs for diploid tumors ranged from 0.7% to 11.9% (median, 3.6%), compared with a range of 1.2% to 26.7% (median, 7.6%) for aneuploid tumors (P < .0001). No significant differences in disease-free or overall survival were observed between patients with diploid and aneuploid tumors. Using different SPF cutoffs by ploidy status (4.4% for diploid, 7.0% for aneuploid), patients with low SPFs had significantly longer disease-free survival rates than patients with high SPFs (P = .0008). The actuarial 5-year relapse rates were 15% and 32% for patients with low (n = 142) and high SPFs (n = 105), respectively. Similar relationships between SPF and clinical outcome were observed for patients with diploid tumors (P = .053) and for patients with aneuploid tumors (P = .0012). Conclusion: S-phase fraction provides additional prognostic information for predicting disease-free survival for axillary node-negative breast cancer patients with small, ER-positive tumors.