Intimal sarcoma of the abdominal aorta with platelet‐derived growth factor receptor α overexpression and amplification in mural invasive cells and pulmonary metastatic cells but not in intimal spreading cells

Intimal sarcoma (IS) is the most common sarcoma of the aorta. The platelet-derived growth factor receptor α (PDGFRA), murine double minute 2 (MDM2), and cyclin-dependent kinase 4 (CDK4) genes are often simultaneously amplified in IS. While immunohistochemical analysis of IS tissue has demonstrated frequent overexpression of the MDM2 and CDK4 proteins, the expression pattern of PDGFRA has not been well characterized, particularly in terms of intratumoral heterogeneity. Here, we present the case of a 46-year-old man who presented with a backache and was subsequently diagnosed with IS. Intratumoral heterogeneity of PDGFRA gene amplification was observed using fluorescence in situ hybridization and was positively correlated with PDGFRA protein expression using immunohistochemistry (IHC). The expression of PDGFRA was also correlated with cytological atypia: PDGFRA was not overexpressed in intimal spreading cells that displayed the lowest degree of atypia while PDGFRA overexpression and amplification were observed in invasive cells of progressive areas such as the aortic wall and a pulmonary metastatic site, which showed increased cytological atypia. Although PDGFRA has not been well examined on IHC, IHC of PDGFRA could be useful to diagnose IS. However, the areas within the tumor from which specimens are derived are important given potential intratumoral heterogeneity.