Abstract DL-1: Molecular Evolution Under Neoadjuvant Chemotherapy
Authors: Børresen-Dale A-L 
Published: May 2016

In the NeoAva study, a randomized phaseII trial of Her2- breast cancer patients (n=132) neoadjuvantly treated with chemotherapy (FEC and taxane) with or without bevacizumab, serial biopsies were obtained; at time of diagnosis, at 12 weeks into treatment and at 25 weeks at surgical removal. High-throughput molecular analyses of DNA, mRNA, miRNA, metabolites using MR spectroscopy (HR-MAS) as well as proteins using RPPA of the serial samples were conducted. Pathological complete response (pCR) in breast and axilla was the primary clinical endpoint. The overall pCR rates were higher in the ER- tumors vs. ER+ tumors, (9 of 23) vs (12 of 109). Addition of bevacizumab seemed to improve pCR in the ER+ patient group (9 vs 3) and not in ER- patient group (5 vs 4).

We studied the different molecular levels separately and combined in order to capture the changes during treatment of the two regimes and correlate the findings to response. Breast tumors are constituted of a number of subclonal populations. Some of these subclones will have stronger resistance to the applied treatment regime than others and will therefore constitute an increasing proportion of the tumor mass as treatment progresses, while sensitive populations will decline. Using the data from the different molecular levels, the subclonal architecture during treatment was evaluated.

Clear subtype specific response to treatment was observed. Luminal A tumors showed a substantial change in gene expression during both treatment periods. In Luminal B and Basal-like tumors, changes were mainly evident during the first treatment period. Bevacizumab enhanced and accelerated the efficacy of chemotherapy in patients with ER+ tumors, and the effect was most evident in patients with Luminal B type. Tumors that achieved pCR showed a significant higher expression of genes enriched for immune response related pathways, compared to the tumors that did not achieve pCR in the ER- group, particularly in tumors from patients treated with chemotherapy combined with bevacizumab. Analyses of selected proteins showed bevacizumab induced changes in expression for several proteins during the treatment period.

MR spectroscopy metabolic profiles at surgery successfully discriminated nonresponders from responders. Additionally, metabolic profiles reflected changes in all patient groups as an effect of chemotherapy. Changes during treatment in responders included reduced levels of choline containing metabolites (involved in cell membrane metabolism) and higher levels of glucose (indicating lower glucose consumption). A reduction of the antioxidant glutathione was associated with the administration of bevacizumab.

Patients displayed substantial differences in observed tumor DNA alterations and tumor percentage over time. In most cases, tumors that retained aberrations at all time points did not increase in size. Signs of subclonal reduction were observed, with some aberrations disappearing and others being retained during treatment.

These results highlight the importance of dissecting the tumor heterogeneity and molecular profile at all levels during tumor evolution under treatment. Even though sequential biopsies are invasive procedures, it could have major impact on patient prediction and prognosis.

Citation Format: Børresen-Dale A-L. Molecular Evolution Under Neoadjuvant Chemotherapy. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr DL-1.