Histiocytoma is a common skin tumor in dogs, especially boxers, and their mixes. But they can happen in any dog. They are some of the least threatening lumps, but they do have the potential to be very serious. They come up rather quickly, and they are itchy, and they gain the attention of the dog. They have a tendency to look quite a bit like a strawberry on the skin, and the dog eventually licks the top of it off.
The lump in the picture, is a classic example of histiocytoma. I took a picture, because nothing looks more like a histiocytoma than this.
You can limit access and stop them from licking these lesions and apply a Cortizone cream like 1% Cortizone 10, once or twice a day for a week before surgery. Just in case it decides to remit and go away with that. Less than one out of 10 will go away on their own, in my clinical experience, but it is worth a try.
If left alone, they can consume too much space for easy removal, additionally, it has been shown that sometimes they spread to other organs, if left alone too long.