Abstract P4-03-01: Budding Tumorigenesis: A novel proposed model for breast cancer tumorigenesis
Authors: Yaghoobi Vesal , Aung Thazin NWE , Moutafi Myrto , Cooke Tyler L , Rimm David L 
Published: March 2022

Abstract
BackgroundDuctal Carcinoma in Situ (DCIS) is a premalignant lesion of breast cancer. However, many of breast cancer cases show no associated DCIS. However, in some cases, we noted some poorly characterized morphologic features, that we believe represent an alternative mechanism of carcinogenesis. Here we show preliminary evidence supporting a novel and unique model for tumorigenesis in breast cancer, that we call budding carcinogenesis, that we believe may be related to breast duct tubule morphogenesis.MethodMany selected H&E slides were examined as well as two newly constructed serial cohorts of breast cancer resected in 2011 and 2012 at Yale New Haven Hospital. We also accessed the Single Cell Expression Atlas (a publicly available dataset) and we used data from a study that performed Single cell RNA-seq of primary breast cancer cells and lymph node metastasis from 11 patients representing the four subtypes of breast cancer: luminal A, luminal B, HER2+ and Triple Negative Breast Cancer (TNBC) to help select potential markers for budding carcinogenesis. We performed multiplex immunofluorescence staining for a set of markers including SPOCK1, A2M, GJA1, SPARC and MMP11 on selected cases from the above cohort. After finalizing the molecular markers using Immunofluorescence microscopy, we tested the generalizability of the selected markers on a Tissue Microarray (TMA) built from serial breast cancer cases. ResultsBreast ducts grow by branching and branching morphogenesis is well described. We observed atypical looking early branches that we hypothesize are the neoplastic extension or usage of the branching process. In this process , we see a proliferation of the outer layer of breast ducts which was associated with change of the axis of nuclei from parallel to the lumen to perpendicular. This change was also associated with lamellipodia formation and mesenchymal transition of the cells in this layer. These morphologic changes are associated with changes at the molecular level including expression of specific markers including SPOCK1 and GJA1 which are otherwise not expressed in the basal layer of normal breast ducts. These changes are associated with a speckling and budding appearance of the basal layer which resulted in separation and dissemination of cells from this layer to the breast stroma. The budding cells were shown to express low CK but high level of SPOCK1, A2M and GJA1 markers. This event is seen with high frequency in many tumors, but so far, does not correlate with a specific breast cancer subtype. ConclusionThese data led us to propose a new tumorigenesis model in which instead of filling the breast ducts lumen as happens in DCIS, cells bud off from the basal layer of breast duct without any breakage in this layer. These budding cells, which come off the ducts, disseminate and seed the invasive tumor, without apparent microinvasion seen as the breakthrough event in traditional DCIS.
Citation Format: Vesal Yaghoobi, Thazin NWE Aung, Myrto Moutafi, Tyler L Cooke, David L Rimm. Budding Tumorigenesis: A novel proposed model for breast cancer tumorigenesis [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P4-03-01.