S-phase fraction and DNA ploidy in 633 T1T2 breast cancers: A standardizedflow cytometric study

The lack of a standardized methodology for quantifying DNA ploidy and S-pha se fraction (SPF) by flow cytometry is hindering routine use of these marke rs in breast cancer management. In a retrospective clinical multicenter stu dy, we validated a standardized flow cytometry protocol. We tested 633 froz en T1T2, N0N1, M-0 breast tumors obtained in four institutions. Cell prepar ation was standardized, and precise rules for data interpretation were foll owed. Three SPF classes were defined on the basis of tertiles after adjustm ent for ploidy, DNA aneuploidy was observed in 61.0% of cases. No significa nt difference was observed among centers. Aneuploidy and high SPF were asso ciated with large tumor size, node involvement, high histological grade, an d hormone receptor negativity. In the overall population (median followup, 69 months), patients with medium and high SPF values had shorter disease-fr ee survival (DFS) than those with low SPF values (P < 0.0001). Ploidy had n o significant influence. By Cox analysis, SPF, pN, and estrogen receptor st atus were independent predictors of DPS (P = 0.0002, P = 0.001, and P = 0.0 5). In node-negative patients, SPF was the only predictor of DFS (P = 0.01) , whereas in node-positive patients, the risk of relapse increased with bot h high SPF (P = 0.003) and estrogen receptor negativity (P = 0.004), Low SP F values distinguished grade II tumors with a particularly good outcome. Ou r results strongly support the use of SPF in multicenter studies and clinic al trials and suggest that node-negative patients with slowly proliferating tumors do not require systemic adjuvant therapy.