Dog paw lump

Hi everyone, My 3-year-old Pomsky has had a small bump between his toes (next to one of the small paw pads, not near the nail/claw) for about 1 month. I took him to the vet, and they examined it. They sent us home with antibiotics and then an anti-inflammatory (Rimadyl) and said if it doesn’t improve, they want me to come back next week to rule out something more serious, including possibly cancer. He has no limp, doesn’t seem to be in pain when I touch it, and still walks normally. The bump doesn’t seem to have changed much, although I’ve noticed some tiny red spots around it. The claw looks normal. He normally walks around 4 miles a day (split into multiple walks), but I’ve limited his walks over the last few days to see if reducing the friction helps. My follow-up appointment is in 1 week, and I’m honestly really worried. Based on the photos, what do you guys think? Does this look more like an interdigital cyst or inflammation, or does it look concerning for a tumor? Has anyone had something similar with their dog? Thank you—I really appreciate any opinions or experiences.