Psoriasis and Lymphoma

Hi everyone, I feel like a bit of a fraud as it's actually my best friend who had severe psoriasis most of his life. My best friend Stewart passed away at only 37 a couple of weeks ago, we'd known each other since we were 4. It's easier to count the times in Stewart's life when his skin wasn't effected by psoriasis and all that comes with that. In the last few years a vicious cycle opened with depression and stress which in turn made his psoriasis worse which in turn made the depression and stress worse and so on. Unknown to everyone he took slightly unwell towards the end of Summer 2019 last year. A lump at the side of his throat and a slight fever that wouldn't shift. Several trips to his Gp who assured him it was vital and rest and fluids were required. At a guess due to the fluctuating nature of depression he stopped asking for help. Fast forward to about 8 weeks ago and he was in a bad way and sought help, went back to gp and sent straight to hospital. Tests, xrays, scans all followed and then about 3 weeks he was due to finally have a biopsy from his swollen neck (by this point his full neck was swollen past his face all the way around) Due to Covid19 and his symptoms being similar his biopsy was put back a week once a negative result was found. He finally got the biopsy on a Thursday and dropped dead three days later. The procurator fiscal said cause of death was undiagnosed and untreated lymphoma. Now I'm certainly no doctor but knowing that both psoriasis and lymphoma are problems with the immune system is there a link ? Especially in a man who had no other health issues and aside his psoriasis lived a healthy life up until this point. Just wondering if anyone had experienced or heard of anything similar ? Thank you for taking the time to read this, still just trying to make sense of a good man taken well before his time.