Molecular changes during extended neoadjuvant letrozole treatment of breast cancer: distinguishing acquired resistance from dormant tumours

Abstract

BackgroundThe risk of recurrence for endocrine-treated breast cancer patients persists for many years or even decades following surgery and apparently successful adjuvant therapy. This period of dormancy and acquired resistance is inherently difficult to investigate; previous efforts have been limited to in-vitro or in-vivo approaches. In this study, sequential tumour samples from patients receiving extended neoadjuvant aromatase inhibitor therapy were characterised as a novel clinical model.MethodsConsecutive tumour samples from 62 patients undergoing extended (4–45 months) neoadjuvant aromatase inhibitor therapy with letrozole were subjected to transcriptomic and proteomic analysis, representing before (≤ 0), early (13–120 days), and long-term (> 120 days) neoadjuvant aromatase inhibitor therapy with letrozole. Patients with at least a 40% initial reduction in tumour size by 4 months of treatment were included. Of these, 42 patients with no subsequent progression were classified as “dormant”, and the remaining 20 patients as “acquired resistant”.ResultsChanges in gene expression in dormant tumours begin early and become more pronounced at later time points. Therapy-induced changes in resistant tumours were common features of treatment, rather than being specific to the resistant phenotype. Comparative analysis of long-term treated dormant and resistant tumours highlighted changes in epigenetics pathways including DNA methylation and histone acetylation. The DNA methylation marks 5-methylcytosine and 5-hydroxymethylcytosine were significantly reduced in resistant tumours compared with dormant tissues after extended letrozole treatment.ConclusionsThis is the first patient-matched gene expression study investigating long-term aromatase inhibitor-induced dormancy and acquired resistance in breast cancer. Dormant tumours continue to change during treatment whereas acquired resistant tumours more closely resemble their diagnostic samples. Global loss of DNA methylation was observed in resistant tumours under extended treatment. Epigenetic alterations may lead to escape from dormancy and drive acquired resistance in a subset of patients, supporting a potential role for therapy targeted at these epigenetic alterations in the management of resistance to oestrogen deprivation therapy.Electronic supplementary materialThe online version of this article (10.1186/s13058-018-1089-5) contains supplementary material, which is available to authorized users.

Influence of pre-operative oral carbohydrate loading vs. standard fasting procedure on tumor proliferation and clinical outcome in breast cancer patients — a randomized trial

“…These processes turn into clinically overt relapses after some years [43]. This is in line with other research, which has found a positive correlation between tumor size and relapse [44], and also between tumor size and development of endocrine resistance [45]. A crucial question is, to what extent the preoperative carbohydrate load to the patients in the present study has promoted the EMT-process in the T2-T3 tumors and thus created more micro metastases [46,47].…”

Early Enrichment of ESR1 Mutations and the Impact on Gene Expression in Presurgical Primary Breast Cancer Treated with Aromatase Inhibitors

“…Tumors with high Ki67r are a very heterogeneous group in our study; however, our findings show that tumors with acquired resistance exhibit smaller changes in gene expression compared with sensitive tumors and that these tumor therefore more closely resemble their diagnostic samples, an observation in keeping with the study from Selli and colleagues (44). Taken together, this supports the notion that the presurgical exposure of ER þ tumors to AI markedly enhances the ability to reveal their dependence on classic ER signaling and therefore identify mechanisms of resistance.…”

Influence of pre-operative oral carbohydrate loading vs. standard fasting procedure on tumor proliferation and clinical outcome in breast cancer patients — a randomized trial

“…These processes turn into clinically overt relapses after some years [43]. This is in line with other research, which has found a positive correlation between tumor size and relapse [44], and also between tumor size and development of endocrine resistance [45]. A crucial question is, to what extent the preoperative carbohydrate load to the patients in the present study has promoted the EMT-process in the T2-T3 tumors and thus created more micro metastases [46,47].…”