The American Society of Clinical Oncology recently convened a panel of medical experts to examine chemotherapy in relation to obese cancer patients. What they found might surprise many: obese patients are routinely underdosed. As it just so happens, as a group they also have higher mortality and recurrence rates.

"There's little doubt that some degree of undertreatment is contributing to the higher mortality and recurrence rates in obese patients," Dr. Gary Lyman, a Duke University oncologist who led the panel, told the Associated Press.

The Study

Before making a recommendation, the medical experts searched the electronic databases of MEDLINE and the Cochrane Collaboration Library in order to identify studies on cytotoxic IV or oral chemotherapy dosing approaches for overweight or obese patients with cancer, excluding leukemias. All of the studies selected by the researchers had been published between 1996 and 2010 and most involved breast, ovarian, colon, and lung cancers. Next, they conducted a systematic review of the literature, which involved, in part, extracting data about treatment toxicity, disease-free survival (DFS), overall survival (OS), and quality-of-life outcomes.

As the American Cancer Society has explained on its website, chemotherapy doses are generally based on either a person’s body weight or a person's body surface area (BSA), which doctors calculate using both height and weight. In addition, chemotherapy is administered at regular intervals known as ‘cycles.’ For chemotherapy to be effective, then, a proper amount must be delivered on an appropriate schedule.

Yet, the panel of medical experts soon discovered that up to 40 percent of obese patients were receiving limited doses not based on their actual body weight. Instead, many oncologists were relying on either ideal body weight or adjusted ideal body weight, or they were capping the body surface area. How this plays out for an obese patient is uncertain. 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," Dr. Jennifer Griggs, a University of Michigan breast cancer specialist and member of the panel, told the Associated Press.

Why, you ask, would oncologists cause a patient such pain?

“Do No Harm”

Because they are afraid of harming their patients by overwhelming their heart and blood system.

"You're three times the size of the average person, but it doesn't mean your heart is," Griggs told the AP. In some cases, too, an obese patient already has diabetes, existing heart troubles, or other illnesses that might make a weight-based amount of chemo too difficult to handle. In short, then, the variation from standard guidelines for chemotherapy dosing is based on very real fears and also very real ignorance as to what an obese person may be able to stand.

The panel, than, has clearly performed a much-needed service by examining this matter and issuing its statement. “The Panel recommends that full weight–based cytotoxic chemotherapy doses be used to treat obese patients with cancer, particularly when the goal of treatment is cure,” wrote the scientists in their paper. They also state no evidence exists that there might be an increase in short-term or long-term toxicity among obese patients receiving full weight-based doses.

In fact, a silver lining may be hidden within the extra weight of obese patients undergoing chemotherapy. A common side effect of treatment is myelosuppression, where the toxicity causes bone marrow activity to falter, which results in fewer red blood cells, white blood cells, and platelets. Here, though, the obese may have an advantage over their thinner fellow patients. “Most data indicate that myelosuppression is the same or less pronounced among the obese than the non-obese who are administered full weight-based doses,” the authors wrote.

Source: Griggs JJ, Mangu PB, Anderson H, et al. Appropriate Chemotherapy Dosing for Obese Adult Patients With Cancer: American Society of Clinical Oncology Clinical Practice Guideline. Journal of Clinical Oncology. 2013.