The Long-HER study: clinical and molecular analysis of patients with HER2+ advanced breast cancer who become long-term survivors with trastuzumab-based therapy

Abstract

Background: Trastuzumab improves survival outcomes in patients with HER2+ metastatic breast cancer. The Long-Her study was designed to identify clinical and molecular markers that could differentiate long-term survivors from patients having early progression after trastuzumab treatment.

Methods: Data were collected from women with HER2-positive metastatic breast cancer treated with trastuzumab that experienced a response or stable disease during at least 3 years. Patients having a progression in the first year of therapy with trastuzumab were used as a control. Genes related with trastuzumab resistance were identified and investigated for network and gene functional interrelation. Models predicting poor response to trastuzumab were constructed and evaluated. Finally, a mutational status analysis of selected genes was performed in HER2 positive breast cancer samples.

Results: 103 patients were registered in the Long-HER study, of whom 71 had obtained a durable complete response. Median age was 58 years. Metastatic disease was diagnosed after a median of 24.7 months since primary diagnosis. Metastases were present in the liver (25%), lungs (25%), bones (23%) and soft tissues (23%), with 20% of patients having multiple locations of metastases. Median duration of response was 55 months. The molecular analysis included 35 patients from the group with complete response and 18 patients in a control poor-response group. Absence of trastuzumab as part of adjuvant therapy was the only clinical factor associated with long-term survival. Gene ontology analysis demonstrated that PI3K pathway was associated with poor response to trastuzumab-based therapy: tumours in the control group usually had four or five alterations in this pathway, whereas tumours in the Long-HER group had two alterations at most.

Conclusions: Trastuzumab may provide a substantial long-term survival benefit in a selected group of patients. Whole genome expression analysis comparing long-term survivors vs. a control group predicted early progression after trastuzumab-based therapy. Multiple alterations in genes related to the PI3K-mTOR pathway seem to be required to confer resistance to this therapy.

Figure 1. Supervised hierarchical clustering for all samples using 1052 differentially expressed probesets identified using SAM.

Each row represents a probeset and each column a sample. Green bars indicate samples from patients in Long-HER group, red bars indicate samples from short-term responders. There are two samples duplicated, * account for metastasis samples.

Figure 2. Signaling pathway annotation enrichment analysis for 858 genes related with trastuzumab resistance.

This analysis was performed using SPEED software. PI3K pathway appeared as the most relevant pathway in relation with trastuzumab resistance.

Figure 3. PI3K-mTOR pathway analyses.

A) Supervised hierarchical clustering for all samples using five genes from the PI3K-mTOR pathway that are differentially expressed between Long-HER and short-term responders to trastuzumab samples. B) Distribution of the normalized expression of these genes.

Figure 4. Mutational status of HER2+ patients.

Distribution of point mutations (red) and copy number variants (blue) in A) genes considered as carriers of cancer driven mutations by Stephens and co-workers, B) genes from the PI3k-mTOR pathway, and C) genes related with trastuzumab resistance (only genes with two of more mutation events are showed, full report is provided as Additional Figure 1). D) Number of point mutations and copy number variants detected in each patient. *This gene is also considered as carrier of cancer driven mutations.

Figure 5. Proposed model of trastuzumab resistance in short-term responders due to Akt/mTOR activation and apoptosis inhibition.

Genes in blue are downregulated, genes in orange are upregulated, genes in red favour Akt/mTOR pathway activation and genes in green decrease Akt/mTOR pathway activation. Red signs are new disrupting elements identified. Green arrow indicates the step regulated by trastuzumab.