Background: Tumor labeling index has emerged as a strong predictor of the clinical course of women with breast cancer. This study investigated whether labeling index of primary tumors correlates with labeling indices of concurrent regional node metastases.
Methods: With appropriate written consent, preoperative in vivo infusion of the thymidine analogue 5-bromodeoxyuridine (BrdUrd) was used to label 109 human breast cancers. Labeled S-phase cells were identified immunohistochemically with an antibody specific to DNA-incorporated BrdUrd. Labeling index was the fraction of labeled nuclei in 2000 tumor nuclei. For 30 women, there was sufficient cancer in axillary lymph nodes to compare labeling indices in primary breast cancer and regional lymph node metastases.
Results: The 30 women were from 25 to 82 years of age. Tumors were from 1 to 12 cm in size and there were from 1 to 26 positive nodes. Tumor labeling index ranged from 0.1% to 34%, (mean, 11.1%; median, 10.3%) and axillary lymph node metastasis labeling index ranged from 0.1% to 27.7% (mean, 10.8%; median, 10.0%). There was strong correlation between primary tumor labeling index and regional lymph node metastases labeling index (r = 0.82, with 95% confidence interval 0.65-0.91). The correlation persisted within subgroups according to age, tumor size, number of positive nodes, and hormone receptor status. Primary tumor and lymph node metastases labeling indices also had statistically similar relationships with age, level of hormone receptors, tumor size, and number of positive nodes.
Conclusions: Primary tumor and regional node labeling indices correlate strongly; the relationship is not influenced by age, level of hormone receptors, tumor size, or number of positive nodes.