The clinicopathologic, immunohistochemical, and flow cytometric characteristics of 34 cases of mammary carcinoma with metaplasia were compared with those of 20 cases of pure sarcoma of the breast. All 20 of the latter tumors showed the pattern of malignant fibrous histiocytoma. There were 20 cases of carcinoma with mesenchymal metaplasia, 7 cases of carcinoma with mixed epithelial (squamous) and mesenchymal metaplasia, and 7 cases of carcinoma with epithelial metaplasia (four mixed ductal/squamous and three pure squamous cell carcinomas). No patient with pure sarcoma had lymph node metastases develop; all nodal metastases were found in patients who had carcinoma with metaplasia, although in one case the carcinomatous component was seen only within a lymph node metastasis. Epithelial antigens were found not only within the epithelial elements of all cases of carcinoma, but also within the apparent mesenchymal elements of 44% of the carcinomas showing divergent differentiation. Flow cytometric analysis of eight cases of carcinoma with mesenchymal metaplasia showed aneuploidy/tetraploidy in six neoplasms. For patient management purposes, the distinction of pure sarcoma from carcinoma with metaplasia is important, but additional subclassification of carcinoma with metaplasia is of greater biologic than clinical interest.

Occlusive vasculopathy with intimal hyperplasia and plexogenic arteriopathy are severe histopathological changes characteristic of pulmonary arterial hypertension (PAH). Although a phenotypic switch in pulmonary endothelial cells (ECs) has been suggested to play a critical role in the formation of occlusive lesions, the pathobiology of this process is poorly understood. The goal of this study was to identify novel molecular mechanisms associated with EC dysfunction and PAH-associated bone morphogenetic protein receptor 2 (BMPR2) deficiency during PAH pathogenesis. A bioinfomatics approach, patient samples, and in vitro experiments were used. By combining a metaanalysis of human idiopathic PAH (iPAH)-associated gene-expression microarrays and a unique gene expression-profiling technique in rat endothelium, our bioinformatics approach revealed a PAH-associated dysregulation of genes involving chromatin organization, DNA metabolism, and repair. Our hypothesis that altered DNA repair and loss of genomic stability play a role in PAH was supported by in vitro assays where pulmonary ECs from patients with iPAH and BMPR2-deficient ECs were highly susceptible to DNA damage. Furthermore, we showed that BMPR2 expression is tightly linked to DNA damage control because excessive DNA damage leads to rapid down-regulation of BMPR2 expression. Moreover, we identified breast cancer 1 (BRCA1) as a novel target for BMPR2 signaling and a novel modulator of pulmonary EC homeostasis. We show here that BMPR2 signaling plays a critical role in the regulation of genomic integrity in pulmonary ECs via genes such as BRCA1. We propose that iPAH-associated EC dysfunction and genomic instability are mediated through BMPR2 deficiency-associated loss of DNA damage control.

Rationale: Idiopathic pulmonary arterial hypertension (IPAH) is a life-threatening disorder characterized by progressive loss of pulmonary microvessels. Although mutations in the bone morphogenetic receptor 2 (BMPR2) are found in 80% of heritable and z15% of patients with IPAH, their low penetrance (z20%) suggests that other unidentified genetic modifiers are required for manifestation of the disease phenotype. Use of whole-exome sequencing (WES) has recently led to the discovery of novel susceptibility genes in heritable PAH, but whether WES can also accelerate gene discovery in IPAH remains unknown.Objectives: To determine whether WES can help identify novel gene modifiers in patients with IPAH.Methods: Exome capture and sequencing was performed on genomic DNA isolated from 12 unrelated patients with IPAH lacking BMPR2 mutations. Observed genetic variants were prioritized according to their pathogenic potential using ANNOVAR. Measurements and Main Results:A total of nine genes were identified as high-priority candidates. Our top hit was topoisomerase DNA binding II binding protein 1 (TopBP1), a gene involved in the response to DNA damage and replication stress. We found that TopBP1 expression was reduced in vascular lesions and pulmonary endothelial cells isolated from patients with IPAH. Although TopBP1 deficiency made endothelial cells susceptible to DNA damage and apoptosis in response to hydroxyurea, its restoration resulted in less DNA damage and improved cell survival.Conclusions: WES led to the discovery of TopBP1, a gene whose deficiency may increase susceptibility to small vessel loss in IPAH. We predict that use of WES will help identify gene modifiers that influence an individual's risk of developing IPAH.