GSTP1 expression predicts poor pathological complete response to neoadjuvant chemotherapy in ER-negative breast cancer

Abstract

The purpose of the present study was to investigate the association of glutathione S-transferase P1 (GSTP1) expression with resistance to neoadjuvant paclitaxel followed by 5-fluorouracil/epirubicin/cyclophosphamide (P-FEC) in human breast cancers. The relationship of GSTP1 expression and GSTP1 promoter hypermethylation with intrinsic subtypes was also investigated. In this study, primary breast cancer patients (n = 123, stage II-III) treated with neoadjuvant P-FEC were analyzed. Tumor samples were obtained by vacuum-assisted core biopsy before P-FEC. GSTP1 expression was determined using immunohistochemistry, GSTP1 promoter methylation index (MI) using bisulfite methylation assay and intrinsic subtypes using DNA microarray. The pathological complete response (pCR) rate was significantly higher in GSTP1-negative tumors (80.0%) than GSTP1-positive tumors (30.6%) (P = 0.009) among estrogen receptor (ER)-negative tumors but not among ER-positive tumors (P = 0.267). Multivariate analysis showed that GSTP1 was the only predictive factor for pCR (P = 0.013) among ER-negative tumors. Luminal A, luminal B and HER2-enriched tumors showed a significantly lower GSTP1 positivity than basal-like tumors (P = 0.002, P < 0.001 and P = 0.009, respectively), while luminal A, luminal B and HER2-enriched tumors showed a higher GSTP1 MI than basal-like tumors (P = 0.076, P < 0.001 and P < 0.001, respectively). In conclusion, these results suggest the possibility that GSTP1 expression can predict pathological response to P-FEC in ER-negative tumors but not in ER-positive tumors. Additionally, GSTP1 promoter hypermethylation might be implicated more importantly in the pathogenesis of luminal A, luminal B and HER2-enriched tumors than basal-like tumors.

Figure 1

Immunohistochemical staining and methylation assay for glutathione S‐transferase P1 (GSTP1). Representative immunohistochemical results for GSTP1 are shown in (A) positive staining and (B) negative staining. Representative results of a real‐time PCR assay for GSTP1 promoter hypermethylation are shown in (C) amplification curves for two samples and seven standards (diluted at 10⁻⁸, 10⁻⁹, 10⁻¹⁰, 10⁻¹¹, 10⁻¹², 10⁻¹³ and 10^−13.5) and in (D) the standard curve for calculation of the copy number.

Figure 2

Glutathione S‐transferase P1 (GSTP1) methylation index according to GSTP1, estrogen receptor (ER), progesterone receptor (PR) and histological grade. Comparison of GSTP1 methylation index (MI) between (A) GSTP1‐positive and GSTP1‐negative tumors, (B) ER‐positive and ER‐negative tumors, (C) PR‐positive and PR‐negative tumors, (D) histological grade 2 (HG2) and HG1 or HG3 tumors in total tumors, (E) HG1 and HG2 tumors in ER‐positive tumors and (F) HG2 and HG3 tumors in ER‐negative tumors. −ve, negative; +ve, positive; bars, median.

Figure 3

Clinical and pathological response to paclitaxel or P‐FEC. Comparison of clinical response to paclitaxel or P‐FEC between glutathione S‐transferase P1 (GSTP1)‐positive and GSTP1‐negative tumors in (A) estrogen receptor (ER)‐positive tumors and (B) ER‐negative tumors. Pathological response to paclitaxel or P‐FEC was also compared between GSTP1‐positive and GSTP1‐negative tumors in (C) ER‐positive tumors and (D) ER‐negative tumors. PAC, paclitaxel; P‐FEC, paclitaxel followed by combined 5‐ fluorouracil/epirubicin/cyclophosphamide; pCR, pathological complete response; −ve, negative; +ve, positive; bars, median.

Figure 4

Glutathione S‐transferase P1 (GSTP1) methylation index (MI), GSTP1 positivity, Ki‐67 labeling index (LI) and pCR rates according to intrinsic subtypes. (A) GSTP1 MI, (B) GSTP1 positivity, (C) Ki‐67 LI and (D) pCR rates are shown by intrinsic subtypes as determined using DNA microarray. bars, median; Basal, basal‐like; HER2, HER2‐enriched; LA, luminal A; LB, luminal B; pCR, pathological complete response.