Feline progressive dendritic histiocytosis, follow-up

In December of 2020 I posted about the aggressive skin cancer — feline progressive dendritic histiocytosis — which was afflicting our large bear-like black cat, Marie. You can read that post here.

Progressive dendritic histiocytosis is unusual in cats. It is more commonly encountered in dogs. Consequently, there is very little material in the veterinary literature about how best to treat it.

In Marie’s case, the surgical removal of the visible large tumors, which took place in November of 2020, had little lasting effect. The site of the largest tumor, now excised, promptly began bulging with a new tumor; one guesses that the excision didn’t get all the cells from that area. By May of 2021, things looked pretty bad again and we took Marie in for a second excision. They checked and there was still no sign of metastasizing to her internal organs, which was one small blessing.

But then, by the mid-to-late fall of 2021, the tumors were back like a bad penny. Red, bulging, oozing and bleeding. Marie’s appetite was undiminished and she showed as much energy as she ever had, which led us to believe that there was again no metastasizing internally. We took her to our local veterinarian who advised us to take her back to the oncologists at Peak Veterinary Referral Center in Williston. The oncologist at Peak said that she did not recommend more surgery; it clearly hadn’t worked. She offered us three options:

1. Steroid therapy
2. Chemotherapy using CCNU (chemo capsule every 4 weeks)
3. Electrochemotherapy: non-surgical way to try to gain local control: may require 2+ treatments for control, can repeat as needed on recurrent or new lesions

We doubted the steroids would work; they hadn’t made any real difference before. Electrochemotherapy — chemo injected into specific locations — seemed unlikely to work because Marie had so many small tumors spread all over. To me, the right option was oral chemotherapy.

Mind you, we had already spent, I don’t know, $4000 or so on all the visits, tests, surgeries, and so on. Most people would probably not spend all that on a cat. I am not most people. As long as Marie’s quality of life was good — eating normally, behaving normally — I saw no reason to consider putting her to sleep. Carole was a lot more cold-blooded about it but I insisted we give it a try. Never mind the expense.

So, we started the oral lomustine (CCNU) in early February.

Four weeks later, the largest tumor had shrunk in size a little but was bulging and bleeding even more. We took her in for another treatment in early March and got her checked out; her white cell count was a little lower than they would have liked so they had us wait two more weeks. She got more chemo at that subsequent visit and the oncologist noted that the tumor had flattened out, though still occasionally bleeding, and that a lot of the small lesions here and there on her body had diminished to the point that we couldn’t feel them. We were worried about the bleeding but we had to trust and hope.

As April went by, we noticed the tumor had entirely flattened out and that skin was starting to grow over the site, a millimeter at a time. The sporadic weeping/oozing/bleeding had basically stopped. That was a very hopeful sign.

Yesterday, when we took her in for her third dose, it really looked a lot better. The oncologist at Peak seemed genuinely surprised by how well it was working — as before, there’s not much out there in the literature to use as a guide and we’d had no idea if this particular chemotherapy regimen was actually going to accomplish anything. But working it was, and there were smiles all around as I left Peak with Marie in her travel carrier.

And that’s where we stand now. She’s scheduled for three more doses of lomustin (CCNU) over the next four months at which time, if all continues to go well, the tumors will be entirely gone and hopefully all the remaining cancer cells will have been obliterated. I imagine that we will need to have her checked pretty frequently afterwards — but “checked” basically means palpating her all over and looking for anything that feels raised or unusual over the skin. All that fur gets in the way of early detection.