The Long-HER Study: Clinical and Molecular Analysis of Patients with HER2+ Advanced Breast Cancer Who Become Long-Term Survivors with Trastuzumab-Based Therapy

<div><p>Background</p><p>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.</p><p>Methods</p><p>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.</p><p>Results</p><p>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.</p><p>Conclusions</p><p>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.</p></div

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

<p>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.</p

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

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

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

<p>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.</p

PI3K-mTOR pathway analyses.

<p>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.</p