Expression of embryonal stem cell transcription factors in breast cancer: Oct4 as an indicator for poor clinical outcome and tamoxifen resistance

Abstract

The transcription factors of embryonic stem cells, such as Oct4, Sox2, Nanog, Bmi1, and Klf4, are known to be associated with stemness, epithelial-mesenchymal transition and aggressive tumor behavior. This study was designed to evaluate the clinicopathological significance of their expression in breast cancer. Immunohistochemistry for Oct4, Sox2, Nanog, Bmi1, and Klf4 was performed in 319 cases of invasive breast cancer. The relationship between the expression of these markers and clinicopathologic features of the tumors, including breast cancer stem cell phenotype and epithelial-mesenchymal transition marker expression, and their prognostic value in breast cancer, were analyzed. Expression of Oct4 and Sox2 was commonly associated with high histologic grade and high Ki-67 index in the whole group and in the hormone receptor-positive subgroup. On the other hand, expression of Nanog, Bmi1, and Klf4 was inversely correlated with aggressive features of the breast cancer. Oct4 expression was associated with ALDH1 expression but not with epithelial-mesenchymal transition marker expression. In survival analysis, Oct4 expression was independently associated with poor prognosis in the whole group and in the hormone receptor-positive subgroup, but not in hormone receptor-negative subgroup. Particularly, Oct4 expression was associated with poor clinical outcome in patients with hormone receptor-positive breast cancer treated with tamoxifen. Our results indicate that Oct4 expression is associated with aggressive features, ALDH1 expression, tamoxifen resistance and poor clinical outcomes in hormone receptor-positive breast cancer, and thus may be useful as a predictive and prognostic marker in this subgroup of breast cancer.

Keywords: Oct4; breast cancer; cancer stem cell; prognosis; tamoxifen resistance.

Figure 1. Representative images of immunohistochemal staining of embryonal stem cell transcription factors

Nuclear staining in 10% or more of the tumor cells is considered as positive for Oct4, Nanog, Bmi1 and Klf4, while nuclear staining in 1% or more of tumor cells is regarded as positive for Sox2 due to the rarity in its expression. Right column represents positive staining of Oct4, Sox2, Nanog, Bmi1, and Klf4 in breast cancer tissues (Original magnification: ×400).

Figure 2. Frequency of Oct4, Sox2, Nanog, Bmi1 and Klf4 expression according to molecular subtype of breast cancer

(A) The frequency of Oct4 expression is significantly lower in luminal A subtype than in luminal B, HER2+ and triple-negative subtypes (luminal A vs. luminal B, p < 0.001; luminal A vs. HER2+, p = 0.001. luminal A vs. triple-negative, p = 0.002). (B) Sox2 expression is less frequent in luminal A subtype than in luminal B and triple-negative subtypes (luminal A vs. luminal B, p = 0.001; luminal A vs. triple-negative, p = 0.020). (C) Nanog is more frequently expressed in luminal A and luminal B subtypes (luminal A vs. HER2+, p = 0.013; luminal A vs. triple-negative, p = 0.043; luminal B vs. HER2+, p = 0.032). (D) Bmi1 expression is more frequent in luminal A and luminal B subtypes than in HER2+ and triple-negative subtypes (luminal A vs. HER2+, p < 0.001; luminal A vs. triple-negative, p < 0.001; luminal B vs. HER2+, p = 0.001; luminal B vs. triple-negative, p = 0.001). (E) Klf4 is more frequently expressed in luminal A and luminal B subtypes than in triple-negative subtype (luminal A vs. triple-negative, p = 0.021; luminal B vs. triple-negative, p = 0.016). LA, luminal A; LB, luminal B; HER2, HER2+; TN, triple-negative.

Figure 3. Disease-free survival according to Oct4 expression

(A) In Kaplan-Meier survival analyses, patients with Oct4 expression have significantly shorter disease-free survival times than those without Oct4 expression in the whole patient group (p = 0.017, log-rank test). (B) Oct4 expression has more significant prognostic value in hormone receptor-positive subgroup (p < 0.001, log-rank test).