Welcome to JustAnswer! I am a licensed veterinarian and would be glad to help!

If you are referring to a lick granuloma for example or a hygroma (pressure sore) - the way to differentiate this from cancer is with a biopsy.

There is no other way.

Some type of aspirate or biopsy would be needed.

There are actually special protector, sleeves for this.

Called Dog Leggs

http://www.dogleggs.com/hygroma/

That should help with these lesions/

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