Spontaneous Extraskeletal Osteosarcoma in the Stomach of an Aged F344 Rat

Extraskeletal osteosarcoma is a very rare tumor in humans and animals including rats. This paper describes a case of extraskeletal osteosarcoma observed in the glandular stomach of an aged female Fischer 344 rat. Grossly, a whitish solid mass was observed at the greater curvature of the glandular stomach. Histologically, the tumor consisted of both atypical polygonal and pleomorphic spindle-shaped cells, with pleomorphic nuclei, and it contained variable amounts of osteoids and small clumps of mature bone tissue. In addition, mitotic figures were frequently observed. Neither invasion of the muscle layer or vessels in the stomach nor metastasis to distant organs was detected. There were no skeletal tumors in the body. Immunohistochemically, the tumor cells were positive for osteocalcin, osteonectin, vimentin and S-100 protein. Judging from these results, the present tumor was diagnosed as extraskeletal osteosarcoma. This is the first report of spontaneous extraskeletal osteosarcoma arising from the stomach in a rat

Transition of Historical Control Data for High Incidence Tumors in F344 Rats

data (from 1990 to 2004, previously reported) in the same facility. In the results, the incidence of C-cell adenoma in the thyroid tended to increase in both sexes in recent years (30.8 % for males and 24.4 % for females in 2005-2009) as compared with the previous data (17.4 % and 20.1 % for males and 11.5 % and 11.8 % for females in 1990–1999 and 2000–2004, respectively). In addition, the incidences of pancreatic islet cell adenoma in males and uterine adenocarcinoma tended to increase from around 2000 and remained high in recent years (incidences of islet cell adenoma in males of 10.5%, 17.1 % and 20.5 % in 1990–1999, 2000–2004 and 2005–2009; incidences of uterine adenocarcinoma of 3.3%, 12.0 % and 13.5 % in 1990–1999, 2000–2004 and 2005–2009, respectively). There was no apparent difference in the incidence of other tumors. (DOI: 10.1293/tox.26.227; J Toxicol Pathol 2013; 26: 227–230) Key words: historical control data, F344 rat, high incidence tumo