Molecular Determinants of Post-Mastectomy Breast Cancer Recurrence

Breast cancer (BC) adjuvant therapy after mastectomy in the setting of 1-3 positive lymph nodes has been controversial. This retrospective Translational Breast Cancer Research Consortium study evaluated molecular aberrations in primary cancers associated with locoregional recurrence (LRR) or distant metastasis (DM) compared to non-recurrent controls. We identified 115 HER2 negative, therapy naïve, T 1-3 and N 0-1 BC patients treated with mastectomy but no post-mastectomy radiotherapy. This included 32 LRR, 34 DM and 49 controls. RNAseq was performed on primary tumors in 110 patients; with no difference in RNA profiles between patients with LRR, DM or controls. DNA analysis on 57 primary tumors (17 LRR, 15 DM and 25 controls) identified significantly more NF1 mutations and mitogen activated protein kinase (MAPK) pathway gene mutations in patients with LRR (24%, 47%) and DM (27%, 40%) compared to controls (0%, 0%; p<0.0001 and p=0.0070, respectively). Three patients had matched primary vs LRR samples, one patient had a gain of a NF1 mutation in the LRR. There was no significant difference between the groups for PTEN loss or cleaved caspase 3 expression. The mean percentage Ki 67 labeling index was higher in patients with LRR (29.2%) and DM (26%) versus controls (14%,p= 0.0045). In summary, mutations in the MAPK pathway, specifically NF1, were associated with both LRR and DM, suggesting that alterations in MAPK signaling are associated with a more aggressive tumor phenotype. Validation of these associations in tissues from randomized trials may support targeted therapy to reduce breast cancer recurrence. This is a multicenter retrospective study of patients who underwent mastectomy at a participating Translational Breast Cancer Research Consortium (TBCRC) institution. Study centers included Memorial Sloan Kettering Cancer Center, University of Pittsburgh, Duke University, Dana Farber Cancer Institute, University of North Carolina at Chapel Hill, Georgetown University, University of Michigan at Ann Arbor, Vanderbilt University, University of Alabama at Birmingham and MD Anderson Cancer Center. Eligible patients included those patients who underwent mastectomy without radiation for T stage 1-3 and N stage 0-1 breast cancer, and for whom archived tissues and outcome data were available. Patients with any recurrence, loco-regional (LRR) or with distant metastasis (DM), were treated from 1997 to present time as this was felt to represent an era when treatment recommendations would be the most uniform and consistent. Patients with LRR could have a subsequent DM as long as this DM was diagnosed at least 3 months after the LRR. Patients who developed LRR after developing distant metastases were placed in the DM group. Control patients were treated from 1997 to 2007 to allow at least five years follow-up with a disease-free interval. Controls were matched to cases for age, ER/PR status, chemotherapy and endocrine therapy regimens and year of diagnosis. All patients were treated with an upfront mastectomy followed by systemic therapy if indicated, which included chemotherapy, endocrine therapy or both. Patients were ineligible if they received post-mastectomy radiation therapy, neoadjuvant chemotherapy, had a T4 primary tumor, N2 nodal disease, were HER2 positive, had positive margins after mastectomy, had fewer than 10 lymph nodes retrieved at axillary lymph node dissection, or had inadequate follow-up (<5 years) if a control patient. If specimens were available from the recurrent tumors, these were also collected for exploratory analysis.