60664
Surgery to remove the tumor is often very difficult due to metastasis into arteries , the esophagus , or the windpipe .
 metastasis
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
Answer:
 metastasis