This is a highly malignant tumour developing in the retina of a baby or infant.


It develops when both the chromosome 13 inherited from the father and the chromosome 13 inherited from the mother are mutated (i.e., two-hit hypothesis).


In some babies, both mutations occur in the same cell, so that only one retinoblastoma develops. Other babies inherit one mutation from a parent, so that every cell in the body is abnormal and so that they tend to develop numerous retinoblastomas in both eyes as well as other cancers in various parts of the body.