I�m assuming the midline he is referring to is the �line� running down the center of the tongue and through the oral cavity. It is my understanding if you have a tumor on the right side, the threat of spread is greatest through the right side of the lymphatic system (lymph nodes in the right side of your neck). The cancer typically doesn�t �cross the midline� and spread from right to left side, unless you�ve already had radiation. I�ve recently been informed by two different doctors that if you had radiation therapy, this can cause fibrosis which could change the course of lymphatic drainage.