Background: Breast cancer has the highest incidence among all female patients 
with different cancer types. It is a lethal disease which threaten women's health. 
There are many prognostic and predictive factors that implicated in breast 
cancer. The expression of Ki-67 is strongly associated with cancer proliferation 
and is a known indicator of breast cancer prognosis and outcome. Ki-67 
expression levels are also useful to inform treatment decision making in some 
cases. As a result, measurement of Ki-67 is routinely done during pathological 
tumor evaluation.
Methods: This study is a prospective study; included eighty-eight of newly 
diagnosed patients presented to the Outpatient Clinic in South Egypt Cancer 
Institute, Assiut University with primary breast carcinoma all of them hormonal 
positive regardless Her2 status. From (1/2022 to 12/2023) before starting 
hormonal treatment and after 6 months of starting treatment. The study was 
approved by the Institutional Review Board of the SECI, Assiut University 
(approval No: 582). An informed written consent was taken from all cases. 
Serum concentration of Ki-67 was measured using a commercially available Ki-
67 ELISA Kit and tissue expression of Ki-67 was assessed by 
immunohistochemical technique.
Results: In this study, clinical significance of serum Ki-67 as a prognostic 
indicator in breast cancer was evaluated among eighty-eight hormone- positive 
early breast cancer cases. More than half of them (56) cases are luminal A breast 
cancer and (32) cases of them are luminal B, no Her2 enriched breast cancer or 
triple negative, more than half of them (55%) received Tamoxifen and (45%) 
received Femara, (31) cases of them are stage I, (37) cases are stage II and (20) 
cases are stage III, more than half of cases showed lower expression of Ki 67, 
Higher expression for ki67 (≥20%) detected in 32 cases. Moreover, the 
relationship between serum Ki-67 by ELISA with clinical, pathologic 
characteristics and patient outcome were detected. 
 Our study showed that the median (range) value of serum Ki-67 was 0.70 
(0.01 – 2.54) ng/ml. serum Ki-67 showed higher median values with increasing 
age, postmenopausal status, increasing tumor size, nodal affection, higher grade, 
estrogen and progesterone receptors positive tumors but of no statistical 
significance. In our study, higher serum Ki-67 level was more frequently 
associated with HER2-positive and it is statistically significant (p value 0.036). 
Our study demonstrated that the median time to progression was 10 months. 
According to Kaplan-Meier analysis, the DFS rate at 20 months was 82.6%. 
Regarding Overall survival: OS was calculated from date of diagnosis till time 
of death from any cause. The median OS couldn't be reached at the end of 
study, no deaths so 1-year OS is 100%.
Conclusion: The results of our study support the finding that serum Ki-67 may 
be considered a valuable biomarker and add a prognostic information to 
classical prognostic factors