Boxer Puppy with soft lump on back

Question
Hi Jannie,
I have a 4 month old male boxer puppy.  We just noticed last night that he has a soft lump on his back.  It is about the size of a small marble and is a little squishy, not hard.  It is under the skin and is not on his spine but off to the side of it on his back.  We just took him to the vet last week and he had a great check up.  I am wondering if we should be concerned.  I know it just came up in the last day or so.  Is he too young for cancer?  Could it just be a cyst?  I am getting worried but wanted to see what you think since a lot of the posts are all of "hard lumps" I was not sure about a soft one.  It does not seem to bother him at all, even when I touch it and try to move it around.
Thank you!

Answer
If it moves, then it is probably a sebaceous cyst.

Read this and let me know if that is probably the lunp:

http://www.petplace.com/dogs/sebaceous-cysts-in-dogs/page1.aspx

If it doesn't fit the description, just phone your vet and talk to him/her or the vet assistant.

I think it's oils that are clogged and formed a cyst.

The vet can lance it and drain it.