Some of the TRAMP prostate tumor cells (even a very small population) were never exposed to sufficient expression of Cre; due to an essential role of FGFR1 in driving prostate tumor progression and metastasis, these FGFR1 intact tumor cells expanded rapidly to give rise to the poorly differentiated primary tumors and provided seeds for metastasis. The gene discussed is FGFR1; the disease is neoplasm.