Postpartum breast cancer has a distinct molecular profile that predicts poor outcomes.

Young women's breast cancer (YWBC) has poor prognosis and known interactions with parity. Women diagnosed within 5-10 years of childbirth, defined as postpartum breast cancer (PPBC), have poorer prognosis compared to age, stage, and biologic subtype-matched nulliparous patients. Genomic differences that explain this poor prognosis remain unknown. In this study, using RNA expression data from clinically matched estrogen receptor positive (ER+) cases (n = 16), we observe that ER+ YWBC can be differentiated based on a postpartum or nulliparous diagnosis. The gene expression signatures of PPBC are consistent with increased cell cycle, T-cell activation and reduced estrogen receptor and TP53 signaling. When applied to a large YWBC cohort, these signatures for ER+ PPBC associate with significantly reduced 15-year survival rates in high compared to low expressing cases. Cumulatively these results provide evidence that PPBC is a unique entity within YWBC with poor prognostic phenotypes.

S-nitrosylated and non-nitrosylated COX2 have differential expression and distinct subcellular localization in normal and breast cancer tissue.

Immunohistochemical (IHC) staining in breast cancer shows both gain and loss of COX2 expression with disease risk and progression. We investigated four common COX2 antibody clones and found high specificity for purified human COX2 for three clones; however, recognition of COX2 in cell lysates was clone dependent. Biochemical characterization revealed two distinct forms of COX2, with SP21 recognizing an S-nitrosylated form, and CX229 and CX294 recognizing non-nitrosylated COX2 antigen. We found S-nitrosylated and non-nitrosylated COX2 occupy different subcellular locations in normal and breast cancer tissue, implicating distinct synthetic/trafficking pathways and function. Dual stains of ~2000 breast cancer cases show early-onset breast cancer had increased expression of both forms of COX2 compared to postmenopausal cases. Our results highlight the strengths of using multiple, highly characterized antibody clones for COX2 IHC studies and raise the prospect that S-nitrosylation of COX2 may play a role in breast cancer biology.

Characterization of weaning-induced breast involution in women: implications for young women's breast cancer.

In rodents, weaning-induced mammary gland involution supports increased mammary tumor incidence, growth, and progression to metastasis. Further, the protumor attributes of gland involution are COX-2 dependent and mitigated by short-duration non-steroidal anti-inflammatory drugs (NSAIDs), suggesting a potential prevention strategy. However, the transition from lactation to postweaning breast involution has not been rigorously evaluated in healthy women. Here we queried breast biopsies from healthy women (n = 112) obtained at nulliparity, lactation, and multiple postweaning time points using quantitative immunohistochemistry. We found that mammary remodeling programs observed in rodents are mirrored in the human breast. Specifically, lactation associates with the expansion of large, secretory mammary lobules and weaning associates with lobule loss concurrent with epithelial cell death and stromal hallmarks of wound healing, including COX-2 upregulation. Altogether, our data demonstrate that weaning-induced breast involution occurs rapidly, concurrent with protumor-like attributes, and is a potential target for NSAID-based breast cancer prevention.

Loss of myoepithelial calponin-1 characterizes high-risk ductal carcinoma in situ cases, which are further stratified by T cell composition.

A hallmark of ductal carcinoma in situ (DCIS) progression is a loss of the surrounding ductal myoepithelium. However, whether compromise in myoepithelial differentiation, rather than overt cellular loss, can be used to predict the risk of DCIS progression is unknown. Here we address this question utilizing pure and mixed DCIS cases (N = 30) as surrogates for DCIS at low and high risk for progression, respectively. We used multiplex immunohistochemical staining to evaluate the relationship between myoepithelial cell differentiation and lymphoid immune cell types associated with poor prognostic DCIS. Our results show that myoepithelial calponin-1 discriminates between pure and mixed DCIS lesions better than histological subtype, presence of necrosis, or nuclear grade. Additionally, focal loss of myoepithelial cells associated with increased PD-1+CD8+ T cells, which suggests a link between the myoepithelium and immune surveillance. To identify associations between calponin-1 expression and immune response, we performed unsupervised hierarchical clustering of myoepithelial and immune cell biomarkers on 219 DCIS lesions from 30 cases. Notably, the majority of pure (low-risk) DCIS lesions clustered in a high calponin-1, T cell low group, whereas the majority of mixed (high-risk) DCIS lesions clustered in a low calponin-1, T cell high group, specifically with CD8+ and PD-1+CD8+ T cells. However, a subset of pure DCIS lesions had a similar calponin-1 and immune signature as the majority of mixed DCIS lesions, which have low calponin-1 and T cell enrichment-raising the possibility that these pure DCIS lesions might be at a high risk for progression.

RNA-seq from archival FFPE breast cancer samples: molecular pathway fidelity and novel discovery.

BACKGROUND: Formalin-fixed, paraffin-embedded (FFPE) tissues for RNA-seq have advantages over fresh frozen tissue including abundance and availability, connection to rich clinical data, and association with patient outcomes. However, FFPE-derived RNA is highly degraded and chemically modified, which impacts its utility as a faithful source for biological inquiry. METHODS: True archival FFPE breast cancer cases (n = 58), stored at room temperature for 2-23 years, were utilized to identify key steps in tissue selection, RNA isolation, and library choice. Gene expression fidelity was evaluated by comparing FFPE data to public data obtained from fresh tissues, and by employing single-gene, gene set and transcription network-based regulon analyses. RESULTS: We report a single 10 µm section of breast tissue yields sufficient RNA for RNA-seq, and a relationship between RNA quality and block age that was not linear. We find single-gene analysis is limiting with FFPE tissues, while targeted gene set approaches effectively distinguish ER+ from ER- breast cancers. Novel utilization of regulon analysis identified the transcription factor KDM4B to associate with ER+ disease, with KDM4B regulon activity and gene expression having prognostic significance in an independent cohort of ER+ cases. CONCLUSION: Our results, which outline a robust FFPE-RNA-seq pipeline for broad use, support utilizing FFPE tissues to address key questions in the breast cancer field, including the delineation between indolent and life-threatening disease, biological stratification and molecular mechanisms of treatment resistance.