Vaa-tumor
this affliction was specific to Yuuzhan Vong master Shapers, and was believed to have been a piece of brain matter of the goddess Yun-Ne'Shel herself. Each Master had to go through a period of personal sacrifice, during which a piece of the Vaa-tumor was implanted in their body. The pain had to be endured, as the Vaa-tumor supposedly altered the Shaper's own cells and brought her closer to Yun-Ne'Shel. After the period of sacrifice, the Vaa-tumor was removed, and the Shaper was changed forever.