Malignancy arising in seminal vesicles in the transgenic adenocarcinoma of mouse prostate (TRAMP) model

BACKGROUND. Transgenic adenocarcinoma of mouse prostate (TRAMP) mice, derived by prostate specific expression of SV40 large T antigen using the rat probasin promoter, all develop prostate tumors akin to human prostate cancers. More recently, epithelial-stromal (ES) tumors resembling phyllodes tumors have been described in the seminal vesicles of TRAMP mice. We report malignancy arising in these ES tumors of the seminal vesicles in TRAMP mice. METHODS. H & E stained sections from 28-week-old TRAMP mice autopsies were examined. Immunostains (cytokeratin, vimentin, desmin, and MIB-1) and electron microscopy were performed on selected blocks of the genitourinary system and metastatic tumor nodules. RESULTS. The seminal vesicles frequently develop tumors containing broad papillae, with bland epithelium and a cellular spindled stroma just beneath the epithelium. The stromal cells have high nuclear to cytoplasmic ratio, frequent apoptotic cells and mitoses. In some cases, the stromal cells become large mass lesions that overgrow the prostate. The epithelium can also proliferate and become malignant. The tumors have high proliferation indices by MIB-1. Some metastatic tumors have characteristics similar to the seminal vesicle ES tumor. CONCLUSIONS. Metastatic tumors in TRAMP mice show three patterns: (1) A definite adenocarcinoma pattern metastatic from the prostate; (2) poorly differentiated tumor without epithelial differentiation; (3) carcinosarcomatous pattern. The carcinosarcomatous pattern and some of the poorly differentiated tumors likely arise from seminal vesicle ES tumors.