Prognostic value of maspin mRNA expression in ER alpha-positive postmenopausal breast carcinomas

Abstract

Maspin, a member of the serpin family, has a role in cell migration, angiogenesis and apoptosis. Little is known of the clinical significance of maspin gene expression in human cancers. We developed a real-time quantitative RT-PCR assay to quantify the full range of maspin mRNA copy numbers in a series of 10 ER alpha-positive and 10 ER alpha-negative breast tumours. We observed a statistical link between low maspin mRNA levels and positive oestrogen status (P=0.0012). In consequence, to better assess the prognostic value of maspin gene expression in breast cancer, we then quantified maspin mRNA content in an additional independent well-defined cohort of 105 ER alpha-positive postmenopausal breast cancer patients treated with primary surgery followed by adjuvant tamoxifen alone. Maspin expression varied widely in tumour tissues (by nearly four orders of magnitude), being underexpressed in 33 out of 105 tumours (31.4%) and overexpressed in 24 out of 105 tumours (22.9%) relative to normal breast tissues. Immunohistochemical studies demonstrated that maspin protein was strictly expressed in myoepithelial cells of normal breast tissue and in tumour epithelial cells, exclusively in maspin-overexpressing tumours. Patients with tumours overexpressing the maspin gene had significantly shorter relapse-free survival after surgery than patients whose tumours normally expressed or underexpressed maspin (P=0.0011). The prognostic significance of maspin overexpression persisted in Cox multivariate regression analysis (P=0.0024). These findings show that the maspin mRNA level can have important prognostic significance in human breast cancer, and point to the maspin gene as a putative molecular predictor of hormone responsiveness in breast cancer.

Figure 1

Immunohistochemical staining for maspin (A, B, E, F) and for myosin heavy chain (C, D) in two breast tumours, one with normal maspin expression (A, C, E) and one with maspin overexpression (B, D, F). Intense maspin immunoreactivity was found in tumour epithelial cells from the maspin mRNA-overexpressing tumour (B) but not in cells (star) from the tumour without maspin overexpression (A) (original magnification × 20). Note the negative myosin heavy-chain staining of tumour epithelial cells from the maspin mRNA-overexpressing tumour (D), confirming that the latter is not of myoepithelial origin (original magnification × 20). In both cases, normal breast tissue showed maspin immunoreactivity in normal myoepithelial cells (arrows) (A, B), which also showed strong immunoreactivity for myosin heavy chain (C, D) (original magnification × 20). Maspin immunoreactivity was localised in the cytoplasmic compartment of both epithelial tumour cells (F) and normal myoepithelial cells (E) (original magnification × 100).

Figure 2

Relapse-free survival curves for patients with maspin-overexpressing, normally expressing and underexpressing tumours.

Figure 3

Relapse-free survival curves in poor-prognosis patient subpopulations (involved lymph nodes >3 (A) and histopathological grade III (B)) according to whether their tumours overexpressed maspin or showed normal/low maspin expression.