Why do you think retinoblastoma only affects the eyes?
I know what retinoblastoma is and that it affects young children, and that is has to do with the 13 chromosome, but does it have to do with the eyes developing first or what?

As you know, it has to do with a gene called RB1 on chromosome 13, which encodes for the retinoblastoma protein. The protein is needed in many cells of the body to inhibit cell division unless the cell is actually ready to divide. Therefore, malfunctioning of this gene can lead to cancer, which is what retinoblastoma is. To answer your question, medical research has actually not yet determined why ONLY eye cancer results from a defect in this gene: "In humans, the protein is encoded by the RB1 gene located on 13q14.1-q14.2. If both alleles of this gene are mutated early in life, the protein is inactivated and results in development of retinoblastoma cancer, hence the name Rb. It is not known why an eye cancer results from a mutation in a gene that is important all over the body." If I had to make a wild guess, I would say that possibly eye cells have only one inhibitor of cell growth - the RB1 protein. In other cells, they may have a variety of cell growth inhibitors that work in conjunction with RB1 to inhibit cell growth. Therefore, the loss of RB1 in other cells of the body is not as dramatic as it is in the eye, and does not lead to cancer. Beyond that, it's a mystery to me!