The DNA labelling index: a prognostic factor in node-negative breast cancer.

The DNA labelling index (LI), representing the fraction of S-phase cells, was studied in 76 patients operated on for breast cancer from 1975 to 1979. No patient had lymph node involvement following axillary dissection (N−), and no adjuvant medical treatment was given. Patients were classified in one of two groups according to the median LI. Patient distribution by age, tumour size, and receptor status was identical in both groups. A higher frequency of grade 3 tumours was noted in the group with an LI above the median value. The cell proliferation rate was an important discriminative factor for metastatic potential. The probability of survival at 8 years for patients with a high LI was significantly lower than that of patients with low LI (36% versus 100%;p<0.001). Relapse-free survival at 8 years was respectively 56% and 83% (p<0.02). At 2 years, these values were 75% and 100%, indicating the early occurrence of metastases. By contrast, the LI had no prognostic value concerning loco-regional disease recurrence or survival after the appearance of metastasis. No relationship was found in this study between survival and other prognostic factors, namely tumour size, histological grade, or hormone receptor level. The LI currently appears to be the best prognostic factor for N− breast cancer. High risk patients identified by this method could thus be offered adjuvant medical treatment.