Thymidine labeling index and estrogen receptor level in 64 human breast cancers.

Concurrent assays of labeling index (LI) and estrogen receptors (ER) have been performed in 64 human breast cancers. The dipping method of autoradiography has been used for measurements of LI. The LI values are given as a number per hundred of cell nuclei labeled by tritiated thymidine. ER levels were determined by dextran-coated charcoal method followed by Scatchard analysis, and expressed in femtomoles per milligram of cytosol protein. Tumours with ER greater than or equal to 28 fmol/mg were demonstrating a low LI (less than 2.3%) and come all from patients of age over 50 years. LI and ER values have been compared with clinical data. The best clinical outcome have been found among patients with low LI values (less than 2.3%). Patients with borderline ER values (3 fmol/mg less than ER less than 28 fmol/mg) showed a satisfactory clinical outcome in 88% of cases when LI less than 2.3% and 57% of cases when LI greater than or equal to 2.3%.