My neighbor's grandchild has trilateral retinoblastoma. what is that exactly?

Retinoblastoma: arises when a patient has two abnormal copies of a tumor suppressor gene. This leads to eye tumors. One gene can be mutated in simple retinoblastoma with the second mutation occurring during retinal development as a spontaneous event. When both copies of the gene are abnormal from the start (germ line mutation) then the risk for trilateral retinoblastoma increases.