Black and blue skin on my cat following chemo?

Hi Vets! I’m just here to get a second opinion. So I’m hoping a vet sees this and is able to answer. A little back story: my 8 year old Maine Coon Norwegian Forest mix kitty was diagnosed with cancer in January. He had gastric mass surgery to remove the tumor in February and we discovered it was large cell lymphoma. He was recovering well after surgery and starting to act like his normal self again, but after his first chemo treatment (COP protocol - cyclophosphamide by pill - no steroids) he got really sick. The day after he received treatment, he had a little blue pigmentation, which has since become darker. I brought him to the oncologist the day after the blue skin started to appear and grow. They did blood work on him - all of which came back normal - and an ultrasound, which revealed he had developed pancreatitis, but otherwise everything looked great. He received treatment for it and has since improved symptoms-wise, but they didn’t know what was causing the blue skin. they assured me it was probably nothing to worry about, but now that it’s gotten darker, I just want to have a second opinion on the matter. Could this just be a rare side effect to the chemo drug he was given? Or could it be a problem that they possibly overlooked? Thanks!

Hello!  - I do not know the answer to this, but feel that it may prove interesting / useful / relevant to find out.  Perhaps you could ask your vet directly to research it for you.  As a practising vet when something appeared that I couldn't identify on one of my cases, people I turned to tended to include relevant drugs companies (eg the chemo drugs companies if licensed or nearly licensed), but also tissue pathologists, who love to chat to vets about cases and might get quite excited about something like this.  They tend to have a wealth of knowledge in their specialist subjects.  I have a vague recollection of skin changes in certain endocrine diseases, drugs reactions or cancers, for example - but a pathologist would be much more objective and could tell your vet whether its worth a biopsy / how best to take it.  I hope that helps.