Hi and thanks for using this forum for your queries.
i am sorry about what your dad is experiencing.
Lumps are very non specific.. They could be several different things. The worst fear is a cancer. It could simply be a lipoma
and sounds more like that.
From the description, it will be rare for this to be cancerous. However, let a medical personnel take a look and consider all the possible options. Make an appointment and at least hear what they have to say. If the answers re not satisfying, you may want to get a picture, post to me and may be follow up with a discussion for me to say more about this to you.
Hope it helps.
Wish your dad good health.
feel free to contact me if need be.