Heterozygous p53+/- transgenic mice are being studied for utility as a short-term alternative model to the 2-yr rodent carcinogenicity bioassay. During a 26-wk study to assess the potential carcinogenicity of
oxymetholone using
p-cresidine as a positive control, glass/
polypropylene microchips (radio transponder identification devices) were subcutaneously implanted into male and female p53+/- mice. During week 15, the first palpable mass was clinically observed at an implant site. This rapidly growing mass virtually quadrupled in size by week 25. Microscopic examination of all implant sites revealed that 18 of 177 animals had a subcutaneous histologically malignant
sarcoma. The
neoplasms were characterized as undifferentiated
sarcomas unrelated to
drug treatment, as indicated by the relatively even distribution among dose groups, including controls. An unusual preneoplastic mesenchymal change characterized by the term "mesenchymal dysplasia" was present in most groups and was considered to be a prodromal change to
sarcoma development. The
tumors were observed to arise from dysplastic mesenchymal tissue that developed within the tissue
capsule surrounding the transponder. The preneoplastic changes, including mesenchymal dysplasia, appeared to arise at the transponder's
plastic anchoring barb and then progressed as a
neoplasm to eventually surround the entire microchip.
Capsule membrane endothelialization,
inflammation, mesenchymal basophilia and dysplasia, and
sarcoma were considered unequivocal preneoplastic/neoplastic responses to the transponder and were not related to treatment with either
oxymetholone or
p-cresidine.