DEAR DR. ROACH: I am a 67-year-old male in good shape. I have Crohn’s disease and have been taking one tablet of mercaptopurine for the past eight years. This is the only medication I take, and if I eat bland, exercise, and keep stress down, I feel good.
I was at the dermatologist, and she had to take biopsies of three possible melanomas. One needs to be cut out, and she sent an email to my gastroenterologist recommending that I stop taking mercaptopurine. My gastroenterologist recommended either infliximab or adalimumab- atto.
Do you think mercaptopurine causes skin cancer, and if you do, which new prescription would you recommend? I don’t want to change medications if I don’t have to. — G.G.
ANSWER: The situation is complicated because people with Crohn’s disease are at an increased risk for melanoma, even without the effects of drugs that modulate the immune system — like all three of the drugs that you’ve mentioned.
It is true that mercaptopurine increases the risk of both melanoma and nonmelanoma skin cancers. But it’s not that these drugs cause skin cancer. The primary risk factor for skin cancer is sunlight, which damages the DNA in skin cells and predisposes people to cancer. The body has systems to repair the DNA, and these can be impaired by mercaptopurine or the other drugs you mentioned, which are both in the class called TNF inhibitors.
There isn’t enough evidence for me to definitively say which has a higher risk, but it appears that TNF inhibitors probably have less of a risk than mercaptopurine. There are not significant differences between infliximab or adalimumab- atto that I can find. The overall risk, even for mercaptopurine, is low; about 1 melanoma was found in 400 people who took the drug for 10 years.
You might ask your gastroenterologist about vedolizumab, which works differently and keeps white blood cells from moving in and causing inflammation in the gut. There doesn’t appear to be an increased cancer risk from this treatment, and it is a preferred treatment in people with a history of cancer.
DEAR DR. ROACH: How can it be that when I weigh myself first thing in the morning, then drink a 1-pound cup of coffee (I weighed it), I weigh more than a pound more afterward? It happens pretty much every day and makes no sense. Weight-wise, I must have expelled more than I took in. I use a digital scale that is accurate. — J.L.
ANSWER: It can’t make sense. While gaining and losing weight sometimes seems to defy common sense, nothing breaks the laws of physics. The scale may be pretty accurate, but it might be very slightly off when adding a pound to your weight. I suspect there may be a rounding error sometimes.
Let’s say you weigh 137.4 pounds, and your scale rounds it down to 137 pounds. Then you drink 16 ounces of coffee, exactly a pound, and you are now 138.4 pounds. If a tiny error occurs where the scale records your weight as 138.6 pounds, for example, your scale will seem to say that you’ve gained two pounds when it rounds your weight up to 139 pounds.
