917
Although Fbxw7 - deficient keratinocytes proliferated excessively in vitro , loss of Fbxw7 did not predispose keratinocytes to the formation of squamous cell carcinoma in vivo induced by the expression of oncogenic Ras , possibly because the stem cell population of keratinocytes becomes exhausted as a result of enhanced Notch activity .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 None