I agree, I would strongly urge my husband to have it checked out in ER, if he were in your husband’s shoes. I wonder if could be a ganglion cyst. I had one on my wrist at one time. It goes away by itself, usually. Though, if it is , I’m surprised that your doctor didn’t bother to tell you what it was, and explain why you had nothing to worry about.

Mine was 3 weeks after BR chemo

Yes. I had that happen. I got an ultrasound which showed a blood clot in the superficial cephalopods vein on the right forearm near my wrist. Because it was in a superficial vein, they had me start taking 325 mg aspirin, try to elevate the arm and use warm compresses. It feels better after two days. Ultrasound is important to determine where the clot is. If it’s in a deep vein, it can require emergency treatment. Have your husband call the oncologist and get an order for an ultrasound asap

Go to the ER.

Hi Linda, so sorry to hear about Mike's cancer diagnosis. You have a lot on your plate. I learned to do things I never thought I would have to do. My husband always took care of everything outside and around the house, until he couldn't.
Cancer sucks , no doubt about it. Don't push yourself too hard. Sending hugs and prayers 🙏🏻
Katie