Validation of existing and development of new prognostic classification schemes in node negative breast cancer

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Abstract
Several prognostic classification schemes in node negative breastcancer are proposed, but only the Nottingham PrognosticIndex (NPI) seems to be sufficiently validated. Validation,which is a prerequisite for a sensible assessment,is not published for two recent proposals accordingto Glick et al. [1] and Rubens [2].The German Breast Cancer Study Group (GBSG) entered662 eligible patients in a prospective observational study.603 of them had complete data for seven’standard‘ prognostic factors and median follow-up is about5 years. As there is no accepted andinformative measure of separation for classification schemes presentlyavailable, we propose a new one and useit additionally to the well known logrank-test andKaplan-Meier estimates to investigate the predictive power ofthe three schemes. Significant differences in survival andrecurrence-free survival could be established for the NPIsubgroups but not for others where even theordering of the groups was different. With theCox model and the classification and regression treeapproach we develop two new proposals for thedifferentiation of subgroups of node negative patients. Asin the NPI, tumor size and grade arethe most important factors, but with a differentweighting scheme. Young age (≤ 40 years) andvery high estrogen receptor values (> 300 fmol)in a small subgroup of patients were associatedwith worse prognosis. The new proposals showed abetter degree of separation, which demonstrates that animprovement seems possible using standard factors. Because themeasures of separation give an overoptimistic impression forthe new proposals, a validation with other studiesis necessary before a general recommendation can begiven.

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