A comparative study of Ki-67 antigen expression between luminal A and triple-negative subtypes of breast cancer

Tumor biomarkers such as hormone receptors, HER-2 and Ki-67 are used routinely in clinical practice for classification of molecular subtypes of breast cancer. Cell proliferation evaluated by Ki-67 antigen expression is important to determine tumor aggressiveness. However, there is a paucity of studies comparing Ki-67 expression in an expressive number of cells among molecular subtypes of breast cancer, particularly among less and more aggressive tumors, such as luminal A and triple-negative, which have led us to the present study. The current study included invasive ductal carcinoma samples of 59 patients, which were divided into two groups: luminal A (n = 29) and triple-negative (n = 30). For immunohistochemical reaction, the samples were incubated with monoclonal anti-Ki-67 antibody (clone MIB1) and cells expressing Ki-67 protein were identified by dark brown staining of the nuclei, counting at least 600 cells per slide. The mean percentages of stained nuclei were analyzed by Student's t test (p < 0.05). The mean percentage of nuclei stained with anti-ki-67 was 10.14 and 77.22 in luminal A and triple-negative breast cancers, respectively (p < 0.0001). Our study showed a high cell proliferation of triple-negative breast cancer in comparison with luminal A, justifying its aggressiveness and poor clinical outcome.