Flow cytometric DNA ploidy defines patients with poor prognosis in node-negative breast cancer

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Abstract
Flow cytometric DNA analysis was performed on fine‐needle aspirates from frozen tumour biopsies from 421 node‐negative, non‐adjuvantly‐treated breast‐cancer patients with a median observation time of 6.75 years. Among premenopausal patients (n = 175), those having at least one DNA “hypoploid” sub‐population defined as DNA index (DI) p = 0.05, Wilcoxon p = 0.007), poor overall survival (OS) (p < 0.001) and poor survival after recurrence (p < 0.001). In the postmenopausal group (n = 246), there were no significant differences among 7 different Dl classes regarding either recurrence‐free survival (RFS) or OS. S‐phase fraction (SPF), divided into quartiles, predicted OS in premenopausal patients only (p = 0.02). Conventional multivariate Cox analysis of OS in the premenopausal group revealed hypoploidy to be the only independent prognostic factor involving a relative risk (RR) of 22.8. Age ≤ 40 years was of marginal significance, whereas SPF, histological grade (WHO), oestrogen and progesterone receptor (PgR) content, tumour size and number of lymph nodes removed were excluded from the model. Application of the conventional Cox model to the premenopausal group regarding RFS was found inappropriate due to lack of proportionality of the hazards of hypoploidy, SPF and histological grade. However, introduction of time‐dependent co‐variates using 2 years as cut‐off level showed hypoploidy with a RR of 3.52 and age ≤ 40 years with a RR of 3.28 to be independent prognostic factors. In the postmenopausal group, the conventional Cox model identified the number of lymph nodes removed to be the only independent prognostic factor regarding RFS as well as OS, whereas SPF < 9% (lowest quartile) was of marginal significance in RFS analysis. Hypoploidy was correlated to high SPF, low PgR content and low differentiation, indicating that hypoploid tumours proliferate rapidly and hormone‐independently. These patients may therefore benefit from adjuvant chemotherapy administered while tumour burden and risk of drug resistance are still low.