Oh Samuel, so sorry, i would have responded earlier if i came across this thread.
It does look more like a disorder of growth (tumour) rather than an inflammatory process like an abscess. However, the only way to be certain is to get a biopsy and get a histopathological analysis.
A lot of tumours are in a dynamic continuum state where something benign one day can develop into something malignant later. Even a benign growth can cause compressional damage to regional organs, nerves and vessels. The trouble with the growth on this axie is that it is located in an awkward position on the body. This growth can impede movement, get ulcerated (due to being abraded on substrate), and prone to subsequent infection.
The best treatment is surgical excision of the lesion and a vet consult is quite necessary.
There is nothing else palliative you can do. There is no neessity for fridging or salt baths etc.
Cheers.