Aldehyde Dehydrogenase 1 Expression in Inflammatory Breast Cancer as Measured by Immunohistochemical Staining

Abstract

Background

Inflammatory breast cancer (IBC) is a rare but aggressive type of breast carcinoma. Despite multimodality approaches, the clinical outcome of patients with IBC remains poor. Tumors arising from cancer stem cells (CSCs) are associated with drug resistance, tumor recurrence, and poor prognosis. This study aimed to evaluate expression of aldehyde dehydrogenase 1 (ALDH1), a putative stem cell marker, in IBC tumors.

Materials and Methods

Tissue microarrays of 74 surgically resected IBC tumors were immunohistochemically stained for ALDH1. The results were correlated with clinicopathologic parameters and survival data and were compared with findings published in the literature.

Results

The median follow-up time of the cohort was 42.1 months, and the 5-year overall survival (OS) rate was 46%. Twenty-four tumors (32%) were positive for ALDH1 staining. However, ALDH1 expression was not significantly associated with clinicopathologic variables, including lymph node status, tumor grade, and the status of estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2. Log-rank testing found that ALDH1 expression was not significantly associated with the OS rate, although there was a trend toward an association with lower OS rate (P = .07). The findings were consistent with some of the published data, but substantial inconsistency among reports was noted.

Conclusion

In this IBC cohort, no significant correlation between ALDH1 expression and prognosis or other clinicopathologic variables was found. Although sample size and selection criteria may be contributory factors, inconsistent results reported in the literature raise concern regarding the reliability of immunohistochemically identified ALDH1 as a sole marker of breast CSCs. Further study is required to elucidate the significance of CSCs in IBC biology.

Introduction

Inflammatory breast cancer (IBC) is a rare but aggressive type of breast cancer.¹ It is characterized clinically by early metastasis and inflammatory-appearing changes of the breast owing to florid lymphovascular invasion of the tumor emboli. Despite multimodality treatment approaches, the clinical outcome of patients with IBC remains poor, with an overall survival (OS) rate of 35% to 40%, which is much lower than that of patients with non-IBC breast cancer.1, 2, 3 Gaining biologic insights into IBC and identifying suitable therapeutic targets are highly desirable.

The cancer stem cell (CSC) concept proposes that cancers arise from a small percentage of tumor cells that possess properties of self-renewal, high proliferation potential, multilineage differentiation, and tumorigenicity. Mounting evidence has indicated that CSCs exist in breast cancer, that they are responsible for tumor resistance to conventional chemotherapy and radiotherapy and for recurrence/metastasis, and that they are more frequently seen in aggressive carcinoma.4, 5, 6

Several putative CSC markers have been evaluated in both preclinical and clinical studies, among which aldehyde dehydrogenase 1 (ALDH1) positivity and the CD44-positive/CD24-negative (CD44⁺/CD24⁻) phenotype are the 2 most commonly used.4, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 ALDH1 is a detoxifying enzyme responsible for oxidizing intracellular aldehydes to carboxylic acids. ALDH1 has a role in the conversion of retinol (vitamin A) to retinoic acid, which is important for proliferation, differentiation, and survival.4, 7, 16 Interestingly, there is no significant correlation between ALDH1⁺ cells and CD44⁺/CD24⁻ cells within the same breast cancer samples, and the overlap between the 2 populations is poor.4, 8, 9, 11, 17 Several studies have suggested that ALDH1 is a better CSC marker than the CD44⁺/CD24⁻ phenotype. For example, Ginestier et al⁴ reported that ALDH1-expressing tumor cells are more tumorigenic than CD44⁺/CD24⁻ tumor cells in immunodeficient mice. In addition, ALDH1 is also involved in metabolizing chemotherapeutic drugs. Significant resistance to sequential paclitaxel- and epirubicin-based chemotherapy was found in tumor cells expressing ALDH1, but not in cells with the CD44⁺/CD24⁻ phenotype.¹¹ A higher ALDH1 level was associated with lower frequency of clinical response to cyclophosphamide-based chemotherapy.¹⁸ Inhibition of ALDH1 activity reduces chemotherapy and radiation resistance in stem-like human breast cancer cell lines.¹⁹ Compared with CD44/CD24 testing, ALDH1 expression can be more readily examined using immunohistochemical (IHC) staining, which is amenable to archival formalin-fixed, paraffin-embedded tissues.4, 8, 10, 11, 17, 20, 21, 22, 23, 24, 25, 26, 27

To date, little is known about the role of CSCs in the biologic behaviors of IBC tumors. In 2008, stem cell signaling pathways such as Notch3 were found to be active in a human IBC xenograft (MARY-X); MARY-X spheroids frequently expressed CD44⁺/CD24⁻, ALDH1, and other CSC phenotypes.²⁸ When testing human IBC samples, they found ALDH1 expression in 10% to 100% of tumor cells within lymphovascular emboli, suggesting that the stem cell–like phenotype may contribute to the aggressive nature of IBC. Charafe-Jauffret et al⁸ reported that ALDH1⁺ cells mediated invasive and metastatic behavior in both IBC cell line (SUM 149) and xenograft (MARY-X) assays. Moreover, the ALDH1⁺ phenotype, but not the CD44⁺/CD24⁻ phenotype, was an independent marker in predicting metastasis in patients with IBC.

If ALDH1 expression is proven to be associated with aggressive clinicopathologic parameters of IBC, therapeutic strategies aimed at targeting ALDH1-expressing cells may be beneficial for these patients. The purpose of the present study was to evaluate ALDH1 expression, using IHC staining, in a cohort of IBC tumors collected at the authors' institution. The results were correlated with clinicopathologic parameters and survival data and were compared with data published in the literature.