Complex sentence: Higashi syndrome ultimately reach a stage known as the "accelerated phase", or the "lymphoma-like syndrome", in which defective white blood cells divide uncontrollably and invade many of the body's organs.
Split into simpler sentences: Higashi syndrome ultimately reach a stage known as the "accelerated phase", or the "lymphoma-like syndrome". In the accelerated phase, defective white blood cells divide uncontrollably and invade many of the body's organs.