Estrogen receptor heterogeneity and the relationship between estrogen receptor and the tritiated thymidine labeling index in human breast cancer.

Tissue from 54 patients with breast cancer was analyzed for estrogen receptor (ER). From 38 patients, tissue from multiple tumor sites was analyzed to determine ER heterogeneity. In 13 patients (34%) both positive and negative ER values were obtained. ER negative (ER-) results were observed more frequently in metastatic lesions. In 28 patients both the ER and [3H]-thymidine labeling index (LI) were measured in the metastatic lesion. [3H]-Thymidine was administered in vivo. There was a positive correlation between ER positivity and low LI. The mean LI of 8 ER positive (ER+) tumors was 3.4 in contrast to a mean LI of 10.0 for 14 ER- tumors (p less than 0.01). LI of 6 mixed ER tumors (ER+/-) was intermediate (mean 5.7). High LI (greater than or equal to 8) was associated with decreased survival regardless of the stage of disease at the time of study. ER with LI may provide an improved basis for treatment selection.