MS & non-hodgkins lymphoma

This is totally suspected correlation and not causation, because we’re not 100% sure, but for some context:

My dad was diagnosed with relapsing MS back in 2009 and was on Tecfidera for about 3 years. I’m not sure exactly why he didnt start medicating way back then (I was 9 when he was diagnosed and my parents didn’t tell me until around 2014), but ik he was on Tecfidera from 2017 or 18-2020.

In 2020, he was diagnosed with non-hodgkins lymphoma and underwent chemotherapy until the end of August 2022. During chemo, his neurologist said he could stop taking the MS medication because chemo would help with prohibiting any new lesions from forming. Although he has been cancer free for 2 years now, he is having relapses again. My mom is concerned that going back on any MS medication will bring back his cancer, and when she spoke to my dad’s neurologist & hematologist about this, they denied that it was because of his medication. I’ve tried telling her there are other treatment options with different ingredients/functions/side effects, but she is still very hesitant.

Has anyone experienced anything like this or have any advice/comments?? Literally anything helps. I love my dad dearly and want the best for him. He’s only 52 and has trouble standing and walking after sitting/laying down for long periods of time, lots of weakness in his legs and occasionally loses feeling in his hand(s). I don’t want things to progress and get worse before it’s too late to go back on medication.

Thanks 🥺