Radiation-Associated Breast Angiosarcoma Versus Recurrent Invasive Ductal Carcinoma After Partial Mastectomy: A Diagnostic Dilemma.

Postradiation angiosarcoma (PRAS) of the breast occurs after irradiation. It is categorized separately from primary angiosarcoma (PAS) in the 2019 World Health Organization classification of tumors. PRAS diagnosis is challenging owing to its occurrence in circumstances similar to breast cancer recurrence, thus complicating cytomorphological analysis. In Japan, breast-conserving therapy is prevalent, with postoperative radiation therapy often employed to mitigate recurrence risk. Given that the number of PRAS cases is anticipated to increase, further research and understanding of this tumor are imperative. Although cytomorphological studies have provided some insights into PAS, similar comprehensive data for PRAS are lacking. In this case study, we report a case of a female in her 50s with a mass detected 8 years postradiotherapy for invasive ductal carcinoma (IDC). Fine needle aspiration cytology (FNAC) initially suggested IDC recurrence; however, histological and immunohistochemical analyses confirmed PRAS. This case highlights the challenge of distinguishing PRAS from IDC owing to overlapping cytomorphological features. Notably, the absence of benign components and distinctive endothelial wrapping observed on FNAC and imprinting cytology were crucial for accurate diagnosis. These findings highlight key cytomorphological features for PRAS differentiation: high-grade tumor features with monotonous appearance and abundant stromal component, which are essential given its poor response to conventional treatments and increasing incidence owing to standard breast-conserving therapies. Furthermore, recognizing PRAS as a differential diagnosis for neoplasms emerging postradiotherapy is crucial.