Tumor-specific HMG-CoA reductase expression in primary premenopausal breast cancer predicts response to tamoxifen

Abstract

Introduction: We previously reported an association between tumor-specific 3-hydroxy-3-methylglutharyl-coenzyme A reductase (HMG-CoAR) expression and a good prognosis in breast cancer. Here, the predictive value of HMG-CoAR expression in relation to tamoxifen response was examined.

Methods: HMG-CoAR protein and RNA expression was analyzed in a cell line model of tamoxifen resistance using western blotting and PCR. HMG-CoAR mRNA expression was examined in 155 tamoxifen-treated breast tumors obtained from a previously published gene expression study (Cohort I). HMG-CoAR protein expression was examined in 422 stage II premenopausal breast cancer patients, who had previously participated in a randomized control trial comparing 2 years of tamoxifen with no systemic adjuvant treatment (Cohort II). Kaplan-Meier analysis and Cox proportional hazards modeling were used to estimate the risk of recurrence-free survival (RFS) and the effect of HMG-CoAR expression on tamoxifen response.

Results: HMG-CoAR protein and RNA expression were decreased in tamoxifen-resistant MCF7-LCC9 cells compared with their tamoxifen-sensitive parental cell line. HMG-CoAR mRNA expression was decreased in tumors that recurred following tamoxifen treatment (P < 0.001) and was an independent predictor of RFS in Cohort I (hazard ratio = 0.63, P = 0.009). In Cohort II, adjuvant tamoxifen increased RFS in HMG-CoAR-positive tumors (P = 0.008). Multivariate Cox regression analysis demonstrated that HMG-CoAR was an independent predictor of improved RFS in Cohort II (hazard ratio = 0.67, P = 0.010), and subset analysis revealed that this was maintained in estrogen receptor (ER)-positive patients (hazard ratio = 0.65, P = 0.029). Multivariate interaction analysis demonstrated a difference in tamoxifen efficacy relative to HMG-CoAR expression (P = 0.05). Analysis of tamoxifen response revealed that patients with ER-positive/HMG-CoAR tumors had a significant response to tamoxifen (P = 0.010) as well as patients with ER-positive or HMG-CoAR-positive tumors (P = 0.035). Stratification according to ER and HMG-CoAR status demonstrated that ER-positive/HMG-CoAR-positive tumors had an improved RFS compared with ER-positive/HMG-CoAR-negative tumors in the treatment arm (P = 0.033); this effect was lost in the control arm (P = 0.138), however, suggesting that HMG-CoAR predicts tamoxifen response.

Conclusions: HMG-CoAR expression is a predictor of response to tamoxifen in both ER-positive and ER-negative disease. Premenopausal patients with tumors that express ER or HMG-CoAR respond to adjuvant tamoxifen.

Figure 1

HMG-CoAR expression is associated with tamoxifen response in vitro. (a) Western blot demonstrating increased expression of 3-hydroxy-3-methylglutharyl-coenzyme A reductase (HMG-CoAR) in tamoxifen-sensitive MCF7 cells compared with their tamoxifen-resistant derivatives LCC9. (b) Quantitative reverse transcriptase PCR demonstrating increased expression of HMG-CoAR mRNA in MCF7 cells compared with LCC9 cells. (c) Immunohistochemistry demonstrating increased HMG-CoAR protein expression in MCF7 cells compared with LCC9 cells. (d) MTT assay demonstrating improved tamoxifen response in MCF7 cells compared with LCC9 cells.

Figure 2

HMG-CoAR mRNA expression is associated with increased recurrence-free survival in tamoxifen-treated breast cancer patients. (a) Mean 3-hydroxy-3-methylglutharyl-coenzyme A reductase (HMG-CoAR) mRNA levels were significantly higher in patients who remained disease-free after tamoxifen treatment. *P < 0.001. (b) Kaplan-Meier using estimates of recurrence-free survival according to HMG-CoAR mRNA expression using mean HMG-CoAR expression as a threshold.

Figure 3

HMG-CoAR protein expression in Cohort II. (a) Immunohistochemical analysis of 3-hydroxy-3-methylglutharyl-coenzyme A reductase (HMG-CoAR) demonstrating different levels of staining intensity. (b) Kaplan-Meier estimates of recurrence-free survival according to HMG-CoAR expression in three groups. (c) Kaplan-Meier estimates of recurrence-free survival according to HMG-CoAR expression (negative = 0 or positive = 1 to 3) in all patients (n = 422).

Figure 4

HMG-CoAR protein expression is associated with tamoxifen response in Cohort II. (a) Kaplan-Meier estimate of recurrence-free survival comparing 2 years of tamoxifen treatment with no adjuvant treatment in 3-hydroxy-3-methylglutharyl-coenzyme A reductase (HMG-CoAR)-negative tumors. (b) Kaplan-Meier estimate of recurrence-free survival comparing 2 years of tamoxifen treatment with no adjuvant treatment in HMG-CoAR-positive tumors. (c) Kaplan-Meier estimate of recurrence-free survival in all estrogen receptor (ER)-positive tumors. (d) Kaplan-Meier estimate of recurrence-free survival in tamoxifen-treated ER-positive tumors. (e) Kaplan-Meier estimate of recurrence-free survival in untreated ER-positive tumors. HR, hazard ratio.

Figure 5

Relationship between estrogen receptor, HMG-CoAR and tamoxifen response in premenopausal breast cancer. (a) Kaplan-Meier estimate of recurrence-free survival based on tamoxifen treatment in estrogen receptor (ER)-positive and 3-hydroxy-3-methylglutharyl-coenzyme A reductase (HMG-CoAR)-positive tumors (n = 141). (b) Kaplan-Meier estimate of recurrence-free survival based on tamoxifen treatment in ER-positive or HMG-CoAR-positive tumors (n = 236). (c) Kaplan-Meier estimate of recurrence-free survival based on tamoxifen treatment in ER-negative and HMG-CoAR-negative tumors (n = 80). (d) Kaplan-Meier estimate of recurrence-free survival in tamoxifen-treated ER-positive patients based on HMG-CoAR expression. (e) Kaplan-Meier estimate of recurrence-free survival in untreated ER-positive patients based on HMG-CoAR expression. HR, hazard ratio.