Conditional Formatting with Partial name search

[Diane]

Is there a way to use conditional formatting to search two lists of names,
and highlight the differences by only highlighing those with last name
differences. (My spreadsheet contains over 250 names)

Example:
Column A:
Jones, Dave
Smith, Bob
Brown, Sally
White, Mary

Column B:
Jones, Dave V.
Smith, Bob A.
White, Mary

I am looking for a conditional formula that would highlight Mary White in
column A as the only different one between the two lists.

Please help.

 

[Teethless mama]

CF:

=COUNTIF($B$2:$B$4,LEFT($A2,FIND(",",$A2))&"*")=0

 

[Diane]

Thanks so much. It worked with one little change to cover the entire list.
=COUNTIF($B:$B,LEFT($A2,FIND(",",$A2))&"*")=0