Molecular Profiling of Aromatase Inhibitor–Treated Postmenopausal Breast Tumors Identifies Immune-Related Correlates of Resistance

Abstract

Purpose: Estrogen withdrawal by treatment with aromatase inhibitors is the most effective form of endocrine therapy for postmenopausal estrogen receptor-positive (ERþ) breast cancer. However, response to therapy varies markedly and understanding of the precise molecular effects of aromatase inhibitors and causes of resistance is limited. We aimed to identify in clinical breast cancer those genes and pathways most associated with resistance to aromatase inhibitors by examining the global transcriptional effects of AI treatment.Experimental Design: Baseline and 2-week posttreatment biopsies were obtained from 112 postmenopausal women with ERþ breast cancer receiving neoadjuvant anastrozole. Gene expression data were obtained from 81 baseline and 2-week paired samples. Pathway analysis identified (i) the most prevalent changes in expression and (ii) the pretreatment genes/pathways most related to poor antiproliferative response.Results: A total of 1,327 genes were differentially expressed after 2-week treatment (false discovery rate < 0.01). Proliferation-associated genes and classical estrogen-dependent genes were strongly downregulated whereas collagens and chemokines were upregulated. Pretreatment expression of an inflammatory signature correlated with antiproliferative response to anastrozole and this observation was validated in an independent study. Higher expression of immune-related genes such as SLAMF8 and TNF as well as lymphocytic infiltration were associated with poorer response (P < 0.001) and validated in an independent cohort.Conclusions: The molecular response to aromatase inhibitor treatment varies greatly between patients consistent with the variable clinical benefit from aromatase inhibitor treatment. Higher baseline expression of an inflammatory signature is associated with poor antiproliferative response and should be assessed further as a novel biomarker and potential target for aromatase inhibitor-treated patients.

Effect of Aromatase Inhibition on Functional Gene Modules in Estrogen Receptor–Positive Breast Cancer and Their Relationship with Antiproliferative Response

“…This is consistent with our recent report showing that immune-related genes are highly predictive of poor antiproliferative response to AIs (12). This is further supported by the recently published article by Tsang and colleagues (43), which showed that higher lymphocytic infiltration correlated with poor prognosis in ER þ patients.…”

“…This anastrozole-treated subgroup constitutes the Functional Aromatase Inhibitor Molecular Study (FAIMoS). Sample acquisition, storage, and RNA extraction was done as previously described (12). Following exclusions, paired samples were available from 81 patients treated for 2 weeks, of which 69 patients had corresponding Ki67 protein expression pre-and post treatment.…”

“…Ki67 is suppressed to a variable extent by AIs in the large majority of breast cancer and overall by a mean of approximately 75% after 2 weeks, increasing to >80% after 12 to 16 weeks (11); the degree of Ki67 suppression by endocrine agents has been found to predict their efficacy as adjuvant therapy. Despite this focus of investigation on proliferation, it is known that many genes not associated with proliferation are also affected by estrogen deprivation (12). It seems likely that these other effects may contribute to the overall impact of AIs on clinical outcome.…”

Molecular Changes in Lobular Breast Cancers in Response to Endocrine Therapy

“…Furthermore, none of the differentially regulated genes highlighted in ILC cell lines and represented in our data (CA12, NEDD9, CXCL12, PDE4B, and NR3C2) were significantly differently regulated between ILC and IDC tumors treated with letrozole (Supplemental Data). Perhaps not surprisingly and consistent with previous studies (12,13), the genes that were most significantly changed in response to letrozole in both ILC and IDC tumors were characterized by downregulation of proliferation and upregulation of ECM remodeling and immune pathways (Fig. 3C).…”

“…To our knowledge, there have been no previous studies on the molecular response to endocrine therapy in ILC patient samples. We and others have characterized the molecular response to endocrine therapy in breast tumors in previous studies (11)(12)(13), but have not previously considered the effects of histologic subtype. Comparing pre-and posttreatment biopsies from the same patients, using the "window of opportunity" afforded with neoadjuvant therapy is a powerful approach that can improve statistical power due to reducing patientpatient variation (14).…”