Thymidine labeling index, flow cytometric S-phase measurement, and DNA index in human tumors. Comparisons and correlations.

The results of flow cytometry were compared with the tritiated thymidine labeling index (TLI) in 314 tumors studied in one laboratory and 163 tumors from a second laboratory, a total of 477, including 306 breast carcinomas. Flow cytometric DNA measurements were obtained on mechanically dissociated fresh tissue stained with propidium iodide or DAPI. Spearman's rank order correlation coefficients (r) for TLI versus flow cytometric S-phase measurement (%S) were 0.38 to 0.55 (P less than 0.001) for diploid DNA index (DNAI) and 0.59 and 0.67 (P less than 0.001) for aneuploid DNAI. The correlations were similar for breast and nonmammary tumors. No correlation of DNAI with TLI or %S was observed for aneuploid tumors, although the aneuploid tumors had significantly higher TLI and %S than diploid tumors (P less than 0.001). Mean TLI for the breast carcinomas was 4.6% and 3.6% for diploid tumors in Series 1 and 2, respectively; for aneuploid tumors, 9.9% and 9.3%. Respective mean %S for diploid breast carcinomas was 6.8% and 7.4%; for aneuploid breast carcinomas, it was 13.6% and 14.5%. The excess of %S over TLI was greatest for tumors with low TLI and appeared to result largely from debris in DNA histograms. TLI, %S and DNAI each predicted both absolute survival and relapse-free survival of breast carcinoma patients.