Lateral differences in Ki-67 in breast cancer

Morphological features of right- and left-sided breast cancer (BC) have been rarely studied. Ki-67 is an independent predictive marker for a local relapse, and for overall and disease-free survival. In previous literature, lateral differences in Ki-67 in BC have not been reported. Using immunohistochemical analysis, the biopsy material of 500 patients was investigated. Four BC parameters were investigated: The expression levels of the estrogen receptor (ER), progesterone receptor (PR), Ki-67 and Her-2-neu. A comparative analysis of Ki-67 in groups with right- and left-sided BC was performed. Lateral differences in Ki-67 in three age groups, ≤49, 50-59 and ≥60 years, were assessed. A higher expression of Ki-67 corresponded with right-sided BC (r=-0.08; P=0.046). Correlation of Ki-67 with the age of the patient was characteristic only for right-sided BC (r=-0.28; P<0.001). The comparative analysis revealed that tumors from patients with right-sided BC aged ≥60 years exhibited a lower Ki-67 index compared with tumors from patients aged ≤49 (P=0.003) and 50-59 years (P=0.000013). In left-sided BC, the Ki-67 in the different age intervals revealed no significant difference. On performing an assessment of lateral differences for the different age intervals, it was established that the Ki-67 index of right-sided BC was significantly higher compared with the left-sided BC in two of the age groups, ≤49 (P=0.038) and 50-59 years (P=0.047). In the ≥60 years group, lateral differences in Ki-67 were not revealed (P=0.4). The analysis of lateral differences in Ki-67 in tumors of various receptor profiles revealed significant differences in Ki-67 of the right- and left-sided BC under ER⁺ PR^- (P=0.007) and ER^- PR^- (P=0.016) conditions. The reasons behind lateral and age differences of Ki-67 are discussed.