1949
This in vitro morphological appearance was exactly reproduced in the in vivo tumors , which were formed when the mixture of A431 and F - 2 cells at the ratio of 10 : 1 were cotransplanted s . c . into the back of nude rats .
 tumors, A431, F - 2 cells, back
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Anatomy 
Text: {0} 
Answer:
 tumors, A431, F - 2 cells, back