The FVB line 19 was a transgenic mouse developed to aid in research into human cervical cancer. The transgenes this particular strain carries are human papillomavirus type 16 E6 and E7 oncogenes. The E6 and E7 oncoproteins exert their affects, at least in part, by association with and inactivation of cellular tumor suppressor gene products including the retinoblastoma susceptibility gene product, Rb. The FVB line 19 has the expression of E6 and E7 targeted to the lens which results in all mice having bilateral cataracts and microphthalmia. The retina is formed from neuroectodermal cells which line the floor of the primitive forebrain.
Retinoblastomas arise from the neuroectoderm of the optic cup.
In this case, the tumor appears to originate at the optic cup and expands into the vitreous chamber, elevating and detaching the retina. The tumor also invades the optic nerve in some sections, a common finding in retinoblastomas. They believe that this tumor is neuroectodermal, but lacks sufficient differentiation to be definitively classified as a retinoblastoma. Thus, a diagnosis of primitive neuroectodermal tumor is favored. The Rb gene is a tumor suppressor gene.