Hi Sis,
Necrosis is death of cells. I was diagnosed in Nov. '05 with squamous cell carcinoma of the right tonsil. The subsequent CT scan showed 4 lymph nodes in my neck with necrotic centers. The tumor board considered these to be cancerous even though they didn't light up a PET. That made me a Stage IV. It was explained to me that a necrotic center is usually cancer so they had to treat it as though it was definitely malignant. This is just my experience with central necrosis. I hope it is better for your sister.
Good luck!
Joe