
With all lumps it is best to get them checked out asap, as even if they are sinister, removed early they can result in complete cure or extend the dogs life to it's normal span.
My Friend recently found a not large lump on her 5 year old dogs side. In fact it was a locally invasive carcinoma resulting in quite a large area being removed.
Now she just goes to have it checked every few months to check for regrowth, as it is the type if not already spread that is likely to reappear in same place.
My bitch had a mammary tumour at five and after removing the pea size lump it didn't reoccur for several years, the next time the whole gland was removed, and she lived to 13 1/2.