Why you should care

Obesity and cancer are already at epidemic proportions, and we might be seeing more cancer patients being undertreated than ever before.

Given the slew of health problems already linked to obesity, recent findings that overweight individuals are less likely to survive cancer probably won’t raise an eyebrow. But one reason might. And it has less to do with obesity than treatment — or rather, undertreatment: Obese patients aren’t given enough chemotherapy.

A common form of treatment for colon, lung, breast and many other cancers, chemotherapy involves a regimen of powerful drugs that kill fast-dividing cells, including tumor cells. But some normal cells also divide quickly — such as those in the hair follicles, mouth and digestive tract — leading to severe nausea and other debilitating side effects for many. More serious complications can include congestive heart failure and leukemia. As a result, physicians limit patients’ chemotherapy dosage based on their body surface area, calculated by plugging their height and weight into a mathematical formula.

The resulting dosage amount might appear alarmingly high for overweight patients, leading doctors to cap it at much lower amounts or to calcuate it based on the ideal weight for the patient’s height, according to a 2013 Nature Reviews Clinical Oncology paper. That could explain why:

As many as

40%

of obese cancer patients receive less than 85% of the right chemotherapy dose for their size.

In the extreme case, these patients might be getting so little chemo that they won’t benefit at all from treatment. Clinical trials for breast cancer, ovarian cancer and lymphoma have found that patients who received less chemotherapy were more likely to relapse or even die from their disease.

Doctors sometimes dial back the dosage for obese patients who have diabetes or heart disease — as many do — since these conditions lower their ability to handle chemotherapy. But earlier studies have shown that obese patients who get the full dose don’t experience side effects any worse than patients who aren’t obese.

The bottom line?

Patients should discuss their chemotherapy regimen with their doctors, including whether they’ll be getting a full dose, advise the Duke University and St. Jude Children’s Hospital researchers who led the study.

In response to these findings, the American Society of Clinical Oncology has adopted a set of guidelines urging doctors to administer the full dosage amount to overweight and obese patients — who now make up a meaningful share of their patient load. A whopping 69.2 percent of adults over age 20 are overweight or obese, according to the CDC.

The dosing issue for obese patients offers just a glimpse of the widespread uncertainty over determining the right chemotherapy regimen for each patient. The biggest reason for this ambiguity? Clinical trials to help determine the starting dose for chemo drugs require participants to have excellent health, excluding not only the obese, but also the elderly and others who are susceptible to severe side effects. The Duke and St. Jude’s researchers suggest relaxing these criteria so doctors can develop treatments that are better tailored to these patient groups.

Overhauling clinical trial requirements is no easy feat. But with obesity and cancer already at epidemic proportions, there’s no better time to start discussing the possibility than now.

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