Complex sentence: In most cases pineal TRb develops before the age of 5, but after the diagnosis of retinoblastoma; non-pineal TRb, however, is often diagnosed simultaneous with retinoblastoma.
Split into simpler sentences: In most cases pineal TRb is diagnosed before the age of 5, but after the diagnosis of retinoblastoma. Non-pineal TRb, however, is often diagnosed simultaneous with retinoblastoma.