Anastomosing Haemangioma: Report of Three Cases With Molecular and Immunohistochemical Studies and Comparison With Well-Differentiated Angiosarcoma.

Anastomosing haemangioma (AH) is a newly described distinct vascular neoplasm that histologically may confuse with well-differentiated angiosarcoma (AS) for those who are unfamiliar with this rare entity. We aimed to identify molecular genetic differences between AHs and ASs by carrying out immunohistochemistry (IHC), fluorescence hybridization (FISH), and next-generation sequencing (NGS). Immunohistochemically, all six cases showed positivity for cyclinD1 and pERK. All cases of AH showed focal weak positive reaction for p53 and MIB-1, and the IHCs for HIF-1α were all negative for all three cases. Those three cases of angiosarcoma revealed strong, diffuse positivity for p53, 50%-70% MIB-1 labelling, and multifocal, moderate to strong HIF-1α expression. To further clarify the difference in p53 expression, we carried out a FISH which revealed 17p polysomy in all three ASs whereas copy number aberration was absent in the AH group. In one AH case, the c.627G > T nucleotide variant was detected. Due to the rarity and overlapping morphological features, AH might be difficult to separate from other vascular tumours, in particular from well-differentiated AS also featured by mild hyperchromatic, hobnail-like endothelial cells. The potential molecular differences between these two entities presented here may be used in support of the correct diagnosis.