Join Date: Aug 2006
Location: San Francisco Bay Area
Submit Photo: 5
Photo Submissions 19 Times in 13 Posts
I know of two dogs that have had fatty deposits before they were 12 weeks of age (both are Havs), so it is possible, but I think the only way you will ease your mind is to have a veterinarian look at it.
Just out of curiosity, where is it? You said lower back, but if he is standing on all four feet with his back to the sky, is it on that top part of his back, closer to the tail? Most vaccines are given much higher, up by the head. (The two fatty deposits I know about are on the under belly, not the back.)