Loss of constitutive ABCB1 expression in breast cancer associated with worse prognosis

Abstract

ABCB1 gene encodes an adenosine 5′-triphosphate–binding cassette transporter, which not only confers multidrug resistance phenotype in malignant cells, but is also present in several nonmalignant tissues. For the last thirty years, ABCB1 expression in breast cancer has been described by many authors, but the extent of expression differs among the studies, and there is no consensus regarding its potential role in carcinogenesis or in the tumor response to antineoplastic drugs. This study aimed to characterize the expression of ABCB1 in breast tumors as a function of genetic, clinical, and histopathological variables. The ABCB1 expression was also evaluated in nonmalignant mammary tissues adjacent to tumors and in benign lesions. The detection of ABCB1 protein was performed by immunohistochemistry in tissue specimens of excised breasts obtained from a prospective cohort of Brazilian women with breast cancer. The association of ABCB1 protein levels with ABCB1 mRNA, gene polymorphisms, and clinical and histopathological variables was also evaluated. The Kaplan–Meier curves and multivariate Cox regression analyses were conducted to identify independent predictors of disease-free survival of patients with breast cancer. ABCB1 was detected in 86.3% (656) of breast tumors, 98.8% (606) of nonmalignant mammary tissue adjacent to tumors, and 100% (28) of benign lesions. Reduced ABCB1 protein levels in breast tumors was associated with triple-negative subtype (adjusted odds ratio [OR_adj] =0.24; 95% confidence interval [CI] =0.13–0.45), lymph node status < pN2 (OR_adj =0.27; 95% CI =0.10–0.71), tumor size >2 cm (OR_adj =0.55; 95% CI =0.32–0.93), and hypertensive status (OR_adj =0.42; 95% CI =0.24–0.73), and it was significantly associated with shorter disease-free survival, either for all breast cancer patients (p log-rank =0.012; hazard ratio [HR] =3.46; 95% CI =1.21–9.91) or for those with triple-negative tumors (p log-rank =0.007; HR =11.41; 95% CI =1.29–100.67). The loss of constitutive ABCB1 expression in breast cancer, especially in triple-negative tumors, seems to indicate a subgroup of worse prognosis.

Keywords:

• multidrug resistance
• single-nucleotide polymorphisms
• immunohistochemistry
• disease-free survival
• triple-negative breast cancer
• hypertension

Acknowledgments

The authors thank Dr Guilherme Suarez-Kurtz for the use of laboratory facilities and the personnel from the Breast Cancer Hospital, from the Division of Pathology, and from the National Bank of Tumors in the Brazilian National Cancer Institute for logistic support in sample and data collection. This study was supported by grants from Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq 474522/2010-5), Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ E-26/110356/2010), and Instituto Nacional de Ciência e Tecnologia para o Controle do Câncer (CNPq 573806/2008-0; FAPERJ E26/170.026/2008).

Author contributions

JMAD recruited patients, collected clinical and histopathological data, characterized genotypes and haplotypes, helped evaluating patients’ blocks and slides, conducted immunohistochemical and mRNA quantification assays, performed all statistical analyses, generated tables and figures. GMV evaluated surgery resections, selected blocks, and evaluated patients’ slides. VI-do-B recruited patients, collected clinical information, and helped with the statistical analyses. MTSA coordinated the immunohistochemical analyses. TSLS helped recruiting patients and set the genotyping assays. DNP set and performed mRNA expression assays. MSL performed mRNA expression assays and collected histopathological data. MAMC and MAC coordinated mRNA expression assays. RVJ conceived, designed, and coordinated the study; analyzed the data; all authors contributed toward data analysis, drafting and revising the paper and agree to be accountable for all aspects of the work.

Disclosure

JMAD received a PhD scholarship from Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq 140789/2009-0). DNP and MSL received graduate scholarships from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, and TSLS received an undergraduate scholarship from CNPq. The other authors report no conflicts of interest in this work.