Background. Proliferation conveys prognostic information and directs treatment choices in early and especially in estrogen receptor (ER) positive breast cancer. Ki67 is the proliferation marker, which is recommended by the 2013 St Gallen International Breast Cancer Conference to distinguish Luminal A-like from Luminal B-like breast cancer. However, the lack of standardization and absence of a clearly established cut-off value are limitations for the clinical use of Ki67. Recent studies in node negative breast cancer suggest that phosphorylated histone 3 (PPH3) may predict breast cancer death. Our aim was to examine the prognostic role of PPH3 compared to the proliferation markers Ki67, cyclin A and cyclin B1 in node negative breast cancer with a special focus on ER positive disease.
Patients and methods. In a case-control study, we defined 190 women who died from node negative breast cancer as cases and 190 women who were alive at the time for the corresponding case's death as controls. Inclusion criteria were tumor size ≤50 mm, no lymph node metastases and no adjuvant chemotherapy. Of these 380 subjects, 249 had ER positive disease. Tumor tissues were immunostained for PPH3 using commercially available antibodies. The actual number of immunostained cells in 10 fields of view (PPH3 index) and the percentage of immunostained cells counting 200 and 500 tumor cells were calculated.
Results. In node negative patients, PPH3 indexrevealed an odds ratio (OR) for breast cancer death of 2.6 (95% confidence interval (CI) 1.6-4.5 p-value <0.001). PPH3 was strongly correlated to Ki67, histological grade, mitotic count and cyclin A and B1. In ER positive patients the OR for PPH3 index was 2.9 (95% CI 1.6-5.2 p-value <0.001) while the OR for Cyclin A was 3.8 (95% CI 2.2-6.6 p-value <0.001), for cyclin B1 2.9 (95%CI 1.7-4.9 p-value <0.001) and for Ki67 1.6 (95% CI 0.9-4.9 p-value 0,09). However, multivariate analyses showed that cyclin A was the only independent prognostic marker for breast cancer death in ER positive patients, OR 3.6 (95% CI 1.6-8.1 p-value 0.002).
Conclusion. In this study of node negative breast cancer patients, PPH3 showed to be a prognostic factor for breast cancer death. In ER positive patients PPH3 and cyclin A/B1 but not Ki67 could predict breast cancer death. However in the multivariate analysis of proliferation markers, only cyclin A remains as a prognostic factor.
PPH3, phosphorylated histone 3, proliferation, breast cancer, prognostic factor, ER positive