Cancer and multiple sclerosis: what the big studies actually show
Two huge studies — one Canadian, one French — measured cancer risk in people with MS. The picture is nuanced: some risks are slightly higher, some are actually lower. Here is what it means for us.
A few weeks ago a reader sent me a message that worried me: "Nikola, I read somewhere that MS increases cancer risk. Is it true? I'm already fed up with my therapy, and now this." I understand her. When you live with MS, every new threat sounds like the last straw. So I sat down and read both major studies behind the headlines — and honestly, the news is better than the social-media version suggests.
The US National MS Society covered this topic in its Momentum magazine [1](#ref-1), and behind it stand two serious population studies. The first is Canadian, from 2020, led by Dr. Ruth Ann Marrie: it compared 53,984 people with MS to 266,920 people without MS across two Canadian provinces [2](#ref-2) [3](#ref-3). The second is French, from 2024, and even bigger: 140,649 people with MS and 562,596 matched people without MS, followed through ten years of health records [4](#ref-4) [5](#ref-5).
> In short: the overall cancer risk in people with MS is about 6% higher than in everyone else — but that average hides the real picture. Risk is higher for bladder, brain and cervical cancer, and lower for breast, prostate and colorectal cancer.
What exactly is higher, and what is lower
The French study gave the clearest breakdown by cancer type [5](#ref-5). Bladder cancer, brain cancer and cervical cancer were more common in people with MS. Prostate, colorectal and breast cancer were less common. Interestingly, the extra risk was concentrated in people younger than 55; by age 65 it had essentially levelled out with the general population.
The Canadian study added a reassuring nuance about brain cancer: part of that "excess" is probably not a real increase at all, but the fact that people with MS get far more MRI scans — so benign brain tumours that would go unnoticed in others get spotted incidentally [2](#ref-2). Dr. Marrie calls that "overall fairly reassuring" [1](#ref-1).
The bladder deserves special attention
Of everything, bladder cancer worries Dr. Marrie the most — for reasons tied directly to daily life with MS [1](#ref-1). Many of us deal with [bladder problems](/en/blog/sphincters-multiple-sclerosis-manage-bladder-bowel-problems-2026-guide): frequent urinary tract infections, retention, and some of us live with an indwelling catheter. Years of chronic bladder irritation raise the risk.
Practically, that means three things: treat bladder infections promptly and completely instead of "toughing them out"; if you have an indwelling catheter, regular bladder follow-ups are not a luxury but essential protection; and if you ever notice blood in your urine, never write it off as "just MS" without getting it checked. Earlier Canadian research had already pointed to this link [6](#ref-6).
What about the drugs?
This is the question we all ask: does a therapy that dampens the immune system open the door to cancer? The honest answer is — it depends on the drug. Most modern MS therapies have shown no clear cancer-risk signal in the data so far. But some older immunosuppressants carry a known risk: mitoxantrone, rarely used today, is linked to leukaemia, and long-term immune suppression with certain drugs comes with monitoring for specific cancers [7](#ref-7).
That is why a conversation with your neurologist about long-term monitoring is part of the treatment, not paranoia. If you have been on the same drug for years, ask at your next visit: "Are there any specific screening recommendations for my medication?" It is a legitimate question, and a good neurologist will welcome it. You can read more about individual drugs in our [treatment overview](/en/terapija).
The problem the statistics do not show
The French study revealed something else — to me, the most important part of the whole story: people with MS get screened less often than everyone else [5](#ref-5). Not because they do not care, but because the logistics are brutal. A mammogram when you can barely stand. A colonoscopy when your bladder and bowels are unpredictable. Transport to the clinic. Fatigue that eats the whole day. I know this first-hand: an appointment that takes a healthy person an hour takes me a week of planning.
And yet we need screening more than most. Cervical, breast and colorectal cancers caught early are curable in the large majority of cases. The recommendations are clear and age-based [1](#ref-1) [8](#ref-8): a Pap smear roughly every three years, mammograms from age 40–45, colorectal screening from 45, and regular skin checks — especially if you are on immunosuppressive therapy.
What I would tell that reader
First: do not panic. Your overall risk is only slightly higher, and for some of the most common cancers it is actually lower than in people without MS. Second: turn the fear into a calendar. Book the screenings you have been postponing — one at a time, not all at once. Third: if you have a catheter or frequent bladder infections, tell your urologist you have MS and ask how your bladder health should be monitored long term.
MS has taken enough from us already. It should not take our prevention too.
This article is informational and does not replace medical advice. Make decisions about screening and treatment together with your neurologist and your doctor.