Both male and female transgenic mice develop malignant lymphoid tissue and mammary and salivary gland tumors as early as 5 weeks of age. Half of the female transgenic animals develop tumors by 6 months of age. Histological analysis of mammary tumors revealed most of the tumors were adenocarcinomas and were locally invasive with some cases of metastasis to liver and/or lung. The tumors were found to express the transgene transcript. Protein-tyrosine phosphatase epsilon mRNA and protein was found to be highly expressed only in mammary tumors. In 20% of the transgenic mice diffuse benign hyperplasia develops in the Harderian lacrimal gland causing bilateral exophthalmia. Hemizygous transgenic female mice develop tumors by delivery time of first litter with tumorigenesis accelerated by pregnancy. Hemizygous transgenic male mice develop large salivary gland tumors in the neck and eye opacity by 5 to 6 months of age. Hemizygous males have low sperm counts and high incidence of sperm abnormalities resulting in low fertility.