Correlation of bromodeoxyuridine (BRDU) labeling of breast carcinoma cells with mitotic figure content and tumor grade

Tumor proliferation is inversely associated with survival in patients with breast carcinoma. Labeling of tumor cells with bromodeoxyuridine (BRDU) correlates highly with that seen with [3H]thymidine, the current "gold standard" for measuring tumor S-phase. However, the relationship of BRDU labeling to mitotic figure content and tumor grade remains incompletely defined. To determine this, we labeled 55 breast carcinomas with BRDU in vivo and correlated the results with mitotic figure content. The BRDU labeling index was the number of BRDU-positive cells/2,000 tumor cells, the mitotic figure index was the number of mitotic figures per 1,000 tumor cells, and the mitotic figure count was the number of mitotic figures per 10 high-powered fields. BRDU labeling was also correlated with tumor grade (Scarff-Bloom-Richardson). The BRDU labeling index correlated highly with the mitotic figure index (r = 0.814, p = 7.0 x 10(-14)), mitotic figure count (r = 0.725, p = 6.0 x 10(-10)), and tumor grade (r = 0.68, p = 1.1 x 10(-8)). The correlation of BRDU labeling with mitotic figure content was strong enough to suggest that a very carefully measured mitotic figure index provides an estimate of tumor growth fraction equivalent to the BRDU labeling index. Also, analysis of variance showed that the mitotic figure index was twice as precise as the mitotic figure count in estimating BRDU labeling, and thus was a more accurate measure of tumor proliferation. Moreover, measurements made by the mitotic figure index were as precise as those made by BRDU labeling. However, which method is optimal for estimating tumor proliferation rate remains unclear. Further studies are indicated.