Comments on the "Prognostic Impact and Clinicopathological Correlation of CD133 and ALDH1 Expression in Invasive Breast Cancer" and the "Commentary by Antonio Ieni and Giovanni Tuccari"

http://ejbc.kr | pISSN 1738-6756 eISSN 2092-9900 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/ licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. To the Editor, The recent publication by Sung Jeep Kim et al. [1] entitled “Prognostic impact and clinicopathological correlation of CD133 and ALDH1 expression in invasive breast cancer” and the Commentary by Ieni and Tuccari [2] along with the Author’s reply prompted us to share several considerations on the immunodetection of CD133 (Prominin-1) and data regarding its expression in mammary epithelial cells. When assessing the predictive role of CD133 in breast cancer, it is important to consider these data. The authors of both publications fairly discuss the importance of the scoring methods used and the origin of the surgical samples in the observed differences of CD133 immunopositivity rates, and the association of CD133 with breast cancer subtypes or other predictive parameters in several recent studies (Table 1). However, differences may also be attributed to the antibodies used (Table 1). The immunodetection of the pentaspan membrane glycoprotein CD133 has generated discrepancies on numerous occasions. For example, Hermansen et al. [3] have reported inconsistent immunohistochemical patterns on replicates of glioblastoma samples using different anti-CD133 antibodies. Moreover, beyond the fact that variability in the reactivity of polyclonal antibodies is inherent to their production, a given company may market (or may have) several rabbit polyclonal anti-CD133 with distinct specificities. Unfortunately, the description of the antibodies used in these studies is sometimes minimal or incomplete, creating ambiguity about their nature or making it difficult to track information about their precise specificity and to compare the different results [4-6]. In addition, although most studies are very recent, several anti-CD133 antibodies are not commercially available any longer, impeding any further investigation. In some cases, the antibody simply cannot be found with the sellers [7] or is actually specific for a different molecule, E-cadherin [8] (Table 1). Surprisingly, this latter publication by Aomatsu et al. [8] is repeatedly quoted by newer publications, including Kim et al. [1] and Ieni and Tuccari [2], in support of the prognostic role of CD133 in breast cancer [5,9,10]. The specificity of the anti-CD133 antibody is essential for the interpretation of data since the targeted portions of the molecule are in certain cases absent from some splicing variant isoforms [11]. A notable example is the cytoplasmic Cterminal domain of CD133, which constitutes a splicing cassette where alternative and facultative exons are expressed [12]. Therefore, caveats apply to observations made with rabbit antisera against the last 18 amino acids of CD133 as long as the nature of the CD133 isoforms examined is not ascertained (Table 1). Moreover, the glycosylation status of CD133 is known to interfere with the accessibility of certain epitopes, particularly CD133/1, which is recognized by the AC133 monoclonal antibody (Table 1) [13,14]. Therefore, depending on the antibody, one might or not be looking at different entities with potentially different biological and/or pathological roles [15]. When analyzing the expression of CD133 in healthy and pathological samples, two other aspects need to be considered. First, the expression of CD133 is not limited to stem and cancer stem cells. Providing adequate antibodies and immunological techniques (antigen retrieval) are applied, CD133 Comments on the “Prognostic Impact and Clinicopathological Correlation of CD133 and ALDH1 Expression in Invasive Breast Cancer” and the “Commentary by Antonio Ieni and Giovanni Tuccari”