Converting items in the list in the dataframe column to the string in pandas

I have following dataframe containing list in the column

item list      
['ABC','PQR']  
['DEF']        
[]             

I want to add another column called "item".which contains the corresponding string to that list

item list      item   
['ABC','PQR']  ABC,PQR
['DEF']        DEF
[]        

I have tried the following

df["item"]=df["item list"].apply(lambda x:",".join(x))

but it’s giving me wrong answer like th following

item list      item   
['ABC','PQR']  A,B,C,P,Q,R
['DEF']        D,E,F
[] 

I need to get the follwoing answer.How can I achieve it?

item list      item   
['ABC','PQR']  ABC,PQR
['DEF']        DEF
[]