cutting edge vs front line

cutting edge

noun
  • The forefront, or position of greatest advancement in some field. 

  • The sharp edge of the blade of a knife or other cutting tool. 

front line

noun
  • A front, or a boundary between opposing positions. 

  • A low level. 

  • attack, collectively the attackers or forwards. 

  • A site of a conflict, effort, or controversial matter of any kind. 

  • The site of interaction with outsiders, such as customers. 

How often have the words cutting edge and front line occurred in a corpus of books? (source: Google Ngram Viewer )