Spontaneous hemangioendothelial cell hyperplasia of the heart in B6C3F1 female mice.

Spontaneous hemangioendothelial cell hyperplasia of the heart was found in 12 of 3,910 female B6C3F1(C57BL/6CrSlc x C3H/HeSlc) mice that were used in chronic toxicology and carcinogenicity studies at the An-Pyo Center (Shizuoka, Japan). Histologically, the lesions appeared diffusely in the heart as widened vascular spaces lined by a single layer of endothelial-like cells with enlarged nuclei between the muscle fibers. These proliferating cells were identified as hemangioendothelial cells by immunohistochemical techniques, lectin-binding patterns, and electron microscopic examination. Morphological differences were found between this spontaneous hemangioendothelial hyperplasia and that which has been reported as a preneoplastic lesions of hemangiosarcoma. Spontaneous hemangioendothelial cell hyperplasia of the heart occurs rarely; however, it was interesting that spontaneous hemangioendothelial cell hyperplasia was only seen in females with adenocarcinomas of the mammary gland.