Thymidine labeling index and Ki-67 growth fraction in lesions of the breast.

Thymidine labeling index (TLI) and Ki-67 growth fraction (KGF) are two indicators of proliferative activity in breast cancer. The authors examined the relationship between TLI and KGF in 36 breast lesions (28 invasive ductal carcinomas and 8 benign lesions). TLI and KGF values were determined in separately labeled tissue sections as well as in frozen tissue sections labeled with both Ki-67 and tritiated thymidine. In separately labeled sections of carcinoma mean TLI was 6.8 while mean KGF was 16.0. For double-labeled sections of carcinoma mean TLI and KGF values were 6.1 and 16.4, respectively. Strong correlation between TLI and KGF of malignant tumors was found by both methods: r = 0.90 (P less than 0.001) for separately labeled sections, and r = 0.96 (P less than 0.001) for double-labeled sections. In double-labeled sections of benign lesions strong correlation between TLI and KGF also was observed (r = 0.94, P less than 0.001); however, in separately labeled benign breast tissue there was no significant correlation between TLI and KGF (r = 0.38). This may have been the result of variable sampling of small proliferative foci in separate sections of benign breast tissue. The strong correlation between TLI and KGF in breast carcinoma suggests that KGF may have prognostic implications similar to those of the TLI.