Pandas remove character from string in column NOT containing substring

I want to remove "-" in each cell of a column of a dataframe that does not contain "BC".
I do not know how to tweak the following code to "not containing" instead of "containing"
Any help is appreciated.

slate['start'] = slate['start'].astype(str).str.findall('BC'.replace("-",""))
This worked for the inverse case of: replace x with y if cell contains Z.

slate['start'] = slate['start'].astype(str).str.findall(~'BC'.replace("-",""))
I then added the tilde (in my frustration) which clearly did not fork for strings - it yielded a TypeError.
I do not know of any neat way to implement this.

My df is of this "style"

name municipality start end ext x y

0 La Coma Altafulla -200 AD 125 AD 1.74 1.379991 41.154995

You can use pd.Series.where(), which replaces values where the condition (the first argument) is false with the values from the second argument:

slate.start.where(slate.start.str.contains('BC'),
                  slate.start.str.replace('-', ''), 
                  inplace=True)