Expression analysis of CD24 and CD44 transcripts in Iranian breast cancer patients

1. Introduction

Based on the data released by the International Agency for Research on Cancer, breast cancer is the most common cancer among women and the second foremost cause of cancer-related mortality [1]. Several studies have aimed at identification of markers which predict behavior of this type of cancer. Cancer stem cells (CSCs) as a scare population in tumor bulk have the ability to self-renew and differentiate to motivate different pathological events during tumorigenesis [2]. In breast cancer, this population of cells is characterized by high expression of CD44 and low expression of CD24 [3]. Clinical investigations have shown association between the presence of CD44⁺/CD24^−∕low and higher invasion and metastasis capacities of breast cancer [4,5]. Another study in Turkish population demonstrated no significant correlation between CD44 or CD24 expressions and clinicopathologic characteristics. Yet, there was a significant association between CD44⁺/CD24^−∕low phenotype and basal like characteristics as well as EGFR expression [6]. A previous study in Iranian patients reported correlation between down-regulation of BRCA1 expression and CD44⁺ status in breast cancer patients [7]. A recent study has shown the prognostic value of quantification of CD24 and CD44 transcripts in EpCAM+ circulating tumor cells in early stages of breast malignancy [8]. Although the role of CD24 and CD44 as stem cell markers in breast cancer has been well established, the relative abundance of these markers in breast cancer tissues and adjacent non-cancerous tissues (ANCTs) has not been quantified yet.

In the present investigation, we assessed expression of CD24 and CD44 at transcript level in breast cancer tissues and ANCTs in association with clinical determinants of patients’ outcome and parameters that predict response to therapeutic options.

3. Results

3.2. Expression of CD24 and CD44 in breast cancer samples versus ANCTs

Figure 1 shows relative expression levels of CD24 and CD44 in tumoral tissues and ANCTs.

There was no significant difference in expression of CD24 and CD44 in breast cancer tissues compared with ANCTs (Expression ratios: 1.03 and 0.84, P values: 0.92 and 0.61, respectively).

OPEN IN VIEWER

Fig. 1.

Relative expression levels of CD24 and CD44 in tumoral tissues and ANCTs.

3.4. Correlations between expression levels of CD24 and CD44 in different tissues

Expression levels of CD24 and CD44 were correlated with each other in ANCTs (Fig. 2A) but not in tumoral tissues (Fig. 2B).

OPEN IN VIEWER

Fig. 2.

Correlations between expression levels of CD24 and CD44 in ANCTs (A) and tumoral tissues (B).

In the present research, we evaluated expression of two stem cell markers namely CD24 and CD44 in breast cancer tissues and ANCTs. We detected no significant difference in expression of these transcripts between tumoral tissues and ANCTs. Such finding might imply relative abundance of CSCs in the tumoral tissue and the surrounding tissue. However, based on the scarcity of this population of cells in tumoral tissues, this finding should be interpreted with caution.

Notably, we detected association between CD44 expression and tumor size in a way this gene was up-regulated in all of small sized (≤2 cm) tumors compared with the corresponding ANCTs. Besides, CD44 expression was significantly higher in tumors with extracapsular nodal extension compared with those without extension. Consistent with these findings, Horiguchi et al. reported correlation between over-expression of CD44 and smaller tumor size, negative axillary lymph node metastasis and lower stage [9]. Moreover, Bànkfalvi et al. detected correlations between over-expression of CD44 and axillary lymph nodes metastasis of breast cancer [10].

Based on out observations, expression of CD24 was higher in grade 3 tumors compared with grade 2 tumors. However, we did not detect any association between expression of this marker and any other clinical features which is in contrast with Horiguchi et al. who reported correlation between CD24 over-expression and bigger tumor size, lymph node involvement and advanced clinical stage [9]. Moreover, our data regarding expression of CD24 in grade 3 tumors is not consistent with the reported low CD24 expression in breast cancer stem cells and a higher proportion of breast cancer stem cells in tumors with high metastatic potential and recurrences [11]. The probable explanation for this observation is that breast cancer stem cells include a rare population of cells in the tumor. Therefore, the observed expression of CD24 in grade 3 tumors is mostly due to its expression in other cells rather stem cells.

Jang et al. have assessed expression of CD24 and CD44 proteins in breast cancer tissues and reported correlation between CD44 expression and HER2-negative status. On the contrary, CD24 expression was correlated with positivity of HER2. However, they did not report any correlation between expression of these two CSC markers and tumor size, lymph node involvement, tumor stage or grade, or hormone receptors status [12]. Our data regarding higher expression of CD44 and CD24 in tumors with extracapsular nodal extension and grade 3 tumors is in contrast with the results of Jang et al. Moreover, contrary to Jang et al., we demonstrated no significant association between expression of these markers and HER2 status. Although this inconsistency might be at least partly explained by the difference in the method of detection of expression of these markers and source of control tissues, this might also indicate the heterogeneous nature of breast cancer. Consequently, evaluation of expression of these markers in larger sample sizes from different ethnic groups is necessary to appraise their role in the pathogenesis of breast cancer.

Expression levels of CD24 and CD44 were correlated with each other in ANCTs but not in tumoral tissues. This finding might imply the presence of new interactive network between CD24 and CD44 in the tumoral tissues which may influence or be influenced by the presence of malignant features.

Taken together, we demonstrated no significant difference in expression of two CSC markers between breast cancer tissues and ANCTs but associations between expression levels of these transcripts and some of clinical features of breast cancer samples such as tumor size, extracapsular nodal extension and grade. Such associations might imply the role of CD24 and CD44 transcripts in the pathogenesis of this kind of cancer. Based on the unexpected association between expression of CD24 and tumor grade, such effects are possibly not related with their role in the determination of stem cell properties.