Classification of Recurrent MAST and NOTCH Mutations in Breast Carcinoma, a Study of Pre-Malignant Lesions Indicates Early Involvement
Michael R Clay, Varma Sushama, West W Robert. Stanford Hospital and Clinics, Stanford, CA
Background: Recurrent gene fusions and translocations can act as driver mutations affecting tumorigenesis. The Microtubule-Associated Serine/Threonine Kinase family (MAST1-4) is associated with gene fusions that have substantial phenotypic effects in breast epithelial cells. Notch signaling is an evolutionarily conserved pathway that is associated with several inherited developmental diseases, and various types of cancer. Previous studies have identified gene rearrangements in MAST1, MAST2, NOTCH1, and NOTCH2 in 5-7% of invasive breast cancers.
Design: Using tumor microarrays (TMAs), we sought to identify these gene rearrangements in a large series of breast cancers. When rearrangements were identified in carcinoma, we looked to identify earlier stages of involvement. We used probes against the NOTCH1, NOTCH2, MAST1, and MAST2 genes in TMAs containing over 500 cases of breast neoplasia (289 carcinoma in situ, 288 invasive carcinoma, 52 normal). Locus-specific fluorescent in situ hybridization (FISH) was performed using breakapart assays with BACs surrounding target genes. When positive cases were identified on the array, they were analyzed by full section FISH to identify involvement in earlier lesions.
Results: For MAST2 and NOTCH1, FISH was evaluated on 1656 cores from 526 patients, of which 1398 hybridized. Of these, translocations were identified in 12 cases for MAST2 (1.8%) and 9 cases for NOTCH1 (1.3%). Despite multiple attempts, we were unable to generate a successful breakapart probe set for both the MAST1 and NOTCH2 genes. A subset of cases also had amplification, with and without associated translocations. During whole section FISH analysis, when invasive carcinoma was translocated, so were earlier lesions including ductal carcinoma in situ (4/5) and flat epithelial atypia (1/1). No translocations were identified in normal breast tissue, fibrocystic change, or columnar cell change.
Conclusions: We have confirmed the presence of recurrent Mast and Notch family gene rearrangements in breast carcinoma. We have also shown these translocations can be found in precancerous lesions. Knowing at which developmental stage these translocations occur gives further understanding into the complex process of breast tumorigenesis.
Wednesday, March 6, 2013 1:00 PM
Poster Session VI # 23, Wednesday Afternoon