It's impossible for me to say what this lump is. It needs to be checked out by a vet.
It could be benign, something like a fatty tumor (lipoma). If so it may or may not need to be removed. But if it is causing any discomfort, it might be better to have it taken off. If it is cancerous, then it will need to be removed as quickly as possible. Go get it checked, soon as you can.
My red healer/Chow mix is overweight and has lumps Farley large on both shoulder areas, one is larger than the other as well. She is 12 years old. She has smaller ones behind her elbows as well. They feel kind of watery/firm. She doesn't get much exercise because I have a bad back. She try's to get your attention by raising her whole 65 lb body upright, and balancing for quite some time. I wondered if it might be because of doing this and arthritis.