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Background. S-phase fraction (SPF) predicts the prognosis of patients with breast cancer independently of tumor size, axillary metastasis, estrogen receptor (ER) and progesterone receptor (PgR), and patient age. Whether SPF is best measured by DNA labeling index (SPF-LI) or by flow cytometry (SPF-Flow) and what is the relative efficacy of SPF versus histopathologic characteristics for prognosis have remained unanswered questions. Methods. The authors studied 845 women with Stages I-II disease classification for years 1975-1990 with end results data, who were treated surgically with axillary lymph node dissection by an in vitro DNA labeling index protocol with tritiated thymidine or 5-bromo-2'-deoxyuridine and whose SPF was measured microscopically. Nuclear size was estimated with a calibrated optical grid as less than 11[mu]m,11-14[mu]m, or greater than 14 [mu].DNA flow cytometry was performed on fresh or paraffin embedded tissue; ER and PgR were performed by cytosol assay. Kaplan-Meier survival plots and multivariate analysis were used for comparisons. Results. Tumor size, axillary lymph nodal status, SPF-LI, nuclear size, and ER all related strongly to breast cancer specific survival and relapse free survival. PgR was less effective. Lymph node status and tumor size predicted long term survival; differences for other variables largely disappeared by 10 years. By multivariate analysis, axillary lymph node status, tumor size, and ER were independently prognostic for disease specific, relapse free survival. A strong trend was found for nuclear size. PgR, DNA ploidy, and SPF did not contribute to prognosis independently. Nuclear size was the strongest independent predictor in patients with negative axillary lymph nodes. Conclusions. The number of positive axillary lymph nodes, tumor size, ER, and nuclear size were the strongest predictors of prognosis for patients with breast cancer. Only tumor size and lymph node status predicted the long term risk of metastasis. Cancer 1994;74:2287-99.

Background. The S-phase fraction relates to proliferation, an important determinant of tumor behavior, and has been measured most accurately with the DNA precursor tritiated thymidine (TT). The TT labeling index (LI) is a strong stage-independent prognostic indicator for breast carcinoma. The thymidine analogue 5-bromodeoxyuridine (BrdU) is also incorporated into DNA and has the advantage over TT of immunohistochemical detectability rather than requiring autoradiography, but it is less well studied in breast carcinoma. This report demonstrates the equivalence of TT and BrdU LI and explores the relationships between LI and other biologic measurements. Methods. The Ll of 234 consecutive breast carcinomas were measured with TT as was a subsequent series of 450 cases with BrdU, both by incubation in vitro. Results. The mean BrdU LI was 6.4 [+ or -] 0.3% in comparison with 6.9 [+ or -] 0.4% in the prior TT series. Ll was unaffected by storage for 24 hours at 4 [degree] C before labeling with BrdU. The BrdU and TT Ll both correlated (1) positively with tumor size, histologic type, nuclear size, the number of axillary metastases, the level of DNA ploidy, and the percent S-phase by flow cytometry and (2) negatively with the age of the patient and the levels of estrogen receptor and progesterone receptor measured either by ligand binding or by immunohistochemistry. Conclusions. BrdU labeling in vitro was an advantageous method for measuring S-phase fraction in breast carcinoma that produced results comparable to those from TT labeling. It should be equally effective for breast cancer kinetic classification and prognosis and is a suitable standard to evaluate newer methods for measuring cellular proliferation.