How to recode some character values in a dataframe that start with specific letters and numbers?

Question

Let's say I have this df

df = data.frame(x = c("S112","S222","S232","S113","S103","S104"),
                y = c("S115","S242","S252","S117","S108","S110")
                )

I wish to obtain the following result

     x    y
1 lung lung
2 S222 S242
3 S232 S252
4 lung lung
5 lung lung
6 lung lung

The condition is that : for each value that starts with S11 or S10, I wish it to be converted to the value lung