Hi. First, ask for an x-ray. That should be able to determine any cancer or tumors in the paw.
My Chloe is 4 (a rescue at 16 weeks, sad & long story) and has had nail bed infections on and off since 6 months old. They occur for no reason, it's not the seasons or allergies. I spent 4 thousand dollars the first year on her just trying to figure out what was going on. She has them on 3 digits on each of her front paws

They flare up a couple of times a year and sometimes bleed. She is so good though, she doesn't lick them and they don't bother her at all. They looks like little circles right above her nail, but they don't bother her at all.
I took her to two medical vets, a very highly regarded vet hospital in Boston as well as a holistic vet. She was diagnosed with "persistant nail bed infections" that
could lead to cancer. She was on a cycle of meds for 3 years and it held back the infections for a little bit but they always came back. I did food elimination diets, had full allergen testing done, x-rays, scrapings, you name it. All of the vets concluded that she "must just have a genetic disorder" that causes it. She has a low immune system as well so that contributes to them flaring up.
I first put her on a raw diet (Nature's Variety), cut out treats, and cleaned the digits with that blue wash after each walk. The antibiotics were changed around so many times, as she became resistant to some. The last one she was on was $104 for a 48 count bottle! It's insane.
Anyways, what I found that helps the most is one Benedryl a day (as she does have some allergies and I think that contributes to them flaring), Missing Link additive, and soaking her paws every other day in 1 cup of Epsom Salt dissolved in warm water. She's a pug, so it's easy for me to just put her in the sink. I don't know how you would do your Dane.... but it has made such a HUGE difference! The epsom salt is perfectly safe, cheap, and helps ease discomfort if there is any.
I hope it's not cancer for your dog

But I just wanted you to know I have years of experience with nail bed stuff, and I just wanted to share what works for us. Ever since I started Chloe on the Benedryl & epsom salt regimine, she has been clear of infection for 10 months. I don't know if it's that or she is just getting healthier... But I have literally tried everything else out there. Obviously, consult your vet about anything you give to your dog. I find it somewhat humerous that a $4 bottle of benedryl and $2 tub of epsom salt (that lasts me at least 2 months) has done more for her than the hundred dollar pills. My vet is on board with what I'm doing, and she gets check ups 3 times a year with x-rays just to be safe. I know cancer is going to come regardless if she gets benedrly or not, I'm not a fool. But so far, it has helped a great deal in fending off any further infection flares.
Good luck, and let us know how it goes!