How long has the lump been noticeable? If it came up recently and very quickly, it may be nothing more than an insect bite. Spider bites are notorious for causing some pretty spectacular swellings in both humans and animals. When you feel the lump, does it move freely under the skin, or does it seem to be attached to deeper tissues? The reason I ask is that dogs can get all kinds of benign growths at various points in their lives, and those usually can be moved around pretty freely under the skin. As long as the dog isn't biting and clawing at it to the point that the skin is broken, there shouldn't be a problem. If it gets big enough to impair the dog's movement or the dog "worries" at it all the time, it's a simple surgery to have it removed.
I'm glad you're having your vet take a look at it, but it's far more likely to be a benign growth than a malignancy. Stay positive! :-)
In all honesty I've only noticed it for the past few weeks. He'd already been to the vet for a strained back leg where he'd slipped on the laminate floor and I thought it was part of that injury, like a pulled muscle but it does seem to be attached to his chest wall outside the rib cage not the skin. It doesn't seem to bother him in any way. Thank you for your reply I will try and be positive.
Thank you for keeping me positive over the weekend. Thankfully the Vet checked the swelling out today and thought it was a really bad bruise. We'll keep an eye over the next two weeks but he's 90% sure it's not to serious.
Hooray! That's great news, and I'm so glad you didn't torture yourself over the weekend. I'm also glad you went ahead and had your vet check it out. Too many times I've seen folks worry and worry about a possible health issue with their animals, but ultimately refuse to take them to the vet. Ack! :-)