Ki-67 labeling index has been linked to patient outcome in breast cancer patients. However, very few published reports have examined Ki-67 labeling index in African breast cancer patients. Sixty-two Sudanese breast cancer patients with primary invasive tumors were immunostained for Ki-67, ER, PR, Her-2/neu, CK5/6, and CK17. Ki-67 labeling index ranged from 0% to 50%, with a median of 5% (interquartile range 0–10). Low Ki-67 labeling index (immunostaining < 10%) was detected in 43/62 (69.4%) with a median of 0 (interquartile range 0–5), whereas high Ki-67 labeling index (immunostaining ≥ 10%) was revealed in 19/62 (30.6%) with a median of 20 (interquartile range 12–26). Ki-67 labeling index was significantly associated with tumor grade ( , Mann-Whitney Test). There were no significant group differences between Ki-67 labeling index and ER ( ), PR ( ), Her-2/neu ( ), CK5/6 ( ), CK17 ( ), pathologic stage ( ), tumor histology ( ), breast cancer subtypes ( ), tumor size ( ), and age at diagnosis ( ). These results suggested that Ki-67 labeling index correlates with tumor differentiation and not with the tumor size or any other tested marker in Sudanese breast cancers. Thus, Ki-67 labeling index could be considered as a reliable measure of tumor proliferative fraction in Sudan. 1. Introduction The prognosis of breast cancer, a complex and heterogeneous disease [1, 2], depends on several clinical/pathological and biological features such as lymph node (LN) status, tumor size and tumor grade [3–5]; presence or absence of hormone receptors (estrogen (ER) and progesterone (PR)) and other biomarkers, with particular regard to the expression levels of the human epidermal receptor type 2 (Her-2/neu) [6–8]. Data on prognostic biomarkers for breast cancer in indigenous African patients are very scarce due to a number of economic, logistic, and technical reasons [9, 10]. Previously we reported that a breast cancer case series from Khartoum, Central Sudan, was comparable to a breast cancer case series from Milan, Northern Italy, in combined hormone receptors status and breast cancer subtypes [10]. However, relative to the Italian patients, the Sudanese patients were younger and their tumors were larger, of higher grade and more advanced in stage [10]. Furthermore, in this Sudanese series the basal cytokeratins (basal CKs) were expressed in a fraction of cases comparable to those reported for East and West African breast cancer case series, and the combined basal CK positive status was associated with higher grade and inversely correlated with ER, PR, and combined
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