Obese people are less likely to survive cancer, and one reason may be a surprising inequality: The overweight are undertreated.
Doctors often short them on chemotherapy by not basing the dose on a person's size, as they should. They use ideal weight or cap the dose out of fear about how much treatment an obese patient can bear.
Yet, research shows that bigger people handle chemo better than smaller people do.
Even a little less chemo can mean worse odds of survival, and studies suggest that as many as 40 percent of obese cancer patients have been getting less than 85 percent of the right dose for their size.
Now, the largest organization of doctors who treat cancer, the American Society of Clinical Oncology, aims to change that. The group has adopted guidelines urging full, weight-based doses for the obese.
Don't call it supersizing; it's right-sizing cancer care, said Gary Lyman, a Duke University oncologist who led the panel that wrote the advice. "There's little doubt that some degree of undertreatment is contributing to the higher mortality and recurrence rates in obese patients," he said.
The Food and Drug Administration's cancer-drug chief, Richard Pazdur, agrees. "By minimizing the dose, or capping the dose, we have been undertreating patients," he said. The dosing issue applies to all types of cancer treated with chemo: breast, colon, lung, ovarian and even blood diseases such as leukemia.
Giving too little chemo "could make it as if they didn't even get treated at all... so they go through the whole ordeal with no benefit, in the extreme case," said Jennifer Griggs, a University of Michigan breast cancer specialist who also worked on the guidelines.
So why do doctors limit dose?
Sometimes, it's for good reason: The patient has diabetes, heart problems or other illnesses that interfere with how much chemo he can stand. Usually, though, it's because doctors are afraid to follow a standard weight-based formula because the dose seems so huge and they're afraid of harming the heart and blood system, Lyman said.
"You're three times the size of the average person, but it doesn't mean your heart is," Griggs explained.
Yet, studies show that heavier patients are less likely to develop dangerous low blood counts from cancer treatment and that they clear chemo drugs more quickly from the body than thinner people do.
A paper Lyman published in the journal Nature in August said that a 20 percent reduction in chemo doses lowered remission and cure rates by half in animal experiments and helped the tumors develop resistance to the drugs. Other research in people also found lower survival among those getting less chemo.
Even if a patient develops a problem from a chemo treatment and doctors have to dial it back, it's important to try a full dose the next time around so the patient gets all the treatment intended, Lyman said.
Lyman offered this advice to patients: "Ask your doctor how they plan to treat you and whether you're going to get the full dosing. The doctor may have a good reason not to, but you should have that discussion."