information is also valuable when it comes to counseling the family of the patient. DNA analysis can reduce health-care costs by eliminating follow-up evaluations of patients who do not have the germline mutation and their close relatives [10], and it enhances genetic counseling of family members of patients who have the germline mutation and are thus at increased risk of developing retinoblastoma [11]. Fresh tumor samples are necessary to perform the complete genetic testing; thus, adequate planning is necessary when enucleating eyes with unilateral retinoblastoma.

14.5 Pathologic Features

The tumor is composed of small cells with basophilic nuclei, scanty cytoplasm, and numerous mitoses and apoptotic cells. Tumor cells alternate with geographic areas of necrotic tumor cells and deposits of calcium (Fig. 14.2a). The tumor arises from the retina and invades the vitreous, occasionally forming free-floating spheres of tumor seeds. In some tumors, the tumor cells form rosette structures

Fig. 14.2 (a) Histopathologic slide of retinoblastoma demonstrating choroidal invasion (c.i.). Careful assessment must be made in the region of the optic nerve (star) as to whether there is laminar or posterior laminar optic nerve invasion (brackets). (b) High magnification view demonstrating Homer Wright rosette. (c) Gross photo of eye demonstrating combined endophytic and exophytic growth pattern