Track

Clinical Studies

Abstract

Radiation-associated angiosarcomas (RAAS) of the breast may show overlapping histomorphological features with atypical vascular lesions (AVL); particularly in small biopsies with well-differentiated/vasoformative areas and minimal cytological atypia. C-MYC aids in the diagnosis of RAAS if diffusely positive, but focal staining can be challenging to interpret. We evaluated if PRAME shows differential expression in RAAS and AVL and may be helpful to distinguish between these two entities in challenging cases. Ten cases each of AVL and RAAS were evaluated by PRAME immunohistochemistry and graded by percentage of tumor cells labeling as (1+: 0-25%; 2+: 25-50%; 3+: 50-75%; 4+: >75%). H&E stains were reviewed and RAAS were examined for well-differentiated/vasoformative areas. All 10 RAAS cases were C-MYC+ and demonstrated 3+ or 4+ PRAME positivity (>50% tumor cells labeling). All AVLs were PRAME negative. 8/10 (80%) angiosarcomas contained well-differentiated foci which showed PRAME between 2+ and 4+. Two RAAS showed predominantly vasoformative areas without a solid component. One of these cases had initially been diagnosed as AVL because of lack of significant atypia and focal C-MYC labeling; however, a repeat biopsy demonstrated RAAS with solid areas. Retrospective PRAME staining on the original biopsy demonstrated 3+ labeling. Our findings show that PRAME is negative in all cases of AVL, while RAAS show >50% labeling, even in well-differentiated areas of the tumor. Based on the findings in our small series, PRAME may be helpful as an adjunct to C-MYC for supporting a diagnosis of RAAS, particularly in difficult cases with focal c-MYC expression.