Hello, my name isXXXXX and I have over 20 years of experience as a veterinarian.
I'm sorry to hear that Jack has a lump on his foot next to his paw pad and I understand your concern about it.
This may be a benign growth called a histiocytoma.
These growths pop up quickly, grow quickly for a month or so and then tend to regress and resolve on their own within 2 to 3 months. They are most common in
young dogs on the face, ears and legs and paws. But older dogs can get them too
and if they scratch or lick at them they may not resolve.
If the dog licks the mass it will hang around longer or can get infected. You can use a drop of cortisone cream on them to reduce inflammation. If they are scratched open I would recommend an antibacterial ointment instead.
And I would recommend an E-collar for him if he is licking to try and stop him from licking any more. Even if this is a histiocytoma if it doesn't slowly decrease in size or resolve completely in 3 months it should be surgically removed as it is unlikely to go away on its own at that point and can lead to a secondary infection.
Another possibility is a tumor called a mast cell tumor. These have variable degrees of malignancy, some can be treated with just surgical removal, some are quite aggressive and will spread deep into tissue and to local lymph nodes. The only way to know for sure how malignant the tumor is is to remove it and have it biopsied.
Other tumors that this may be include a basal cell tumor but these are much less common in dogs then in people or a melanoma.
These tend to be fairly benign behaving in the skin and respond to surgical
A plasma cell tumor is another possibility.
Of these tumors none resolve completely on their own except a histiocytoma. Mast
cell tumors will change in size if they are bumped, and then go down slightly in size but never fully resolve on their own.
If you want to be absolutely certain of a diagnosis your veterinarian can perform a fine needle aspirate on the bump. He or she puts a tiny needle in the bump, draws cells out, and looks at the cells under the microscope to identify them and give you a tentative diagnosis.
Best of luck with your pup, please let me know if you have any further questions.