Chemotherapy doses should be tailored for obese cancer patients based on their actual body weight, not their ideal body weight, according to a new practice guideline from the American Society of Clinical Oncology.
There is no evidence that full-weight-based chemotherapy doses cause greater toxicity than adjusted doses, and concerns about "overdosing" obese cancer patients are unfounded, a panel of experts wrote in a report published online April 2 in the Journal of Clinical Oncology.
A systematic review of the literature showed that many overweight and obese cancer patients continue to receive underdoses of intravenous and oral cytotoxic drugs because of "considerable uncertainty among physicians about optimal dose selection," even though research has confirmed that full-weight-based dosing is both safe and crucial to the patients’ survival.
"Many oncologists continue to use either ideal body weight or adjusted ideal body weight, or to cap the body surface area at, for example, 2.0 m2, rather than use actual body weight to calculate body surface area," said Dr. Jennifer J. Griggs of the University of Michigan, Ann Arbor, and her associates on the expert panel for ASCO’s new practice guideline.
As a result, chemotherapy dosing varies widely in overweight and obese patients, with as many as 40% receiving less than optimal dosing. This "may explain, in part, the significantly higher cancer mortality observed in overweight and obese individuals," they noted.
"With the incidence of obesity at an all-time high in the United States, as well as in other developed and developing nations, oncologists face this issue more than ever before," Dr. Griggs added in a press statement accompanying release of the guideline.
The ASCO guideline panel reviewed all the randomized clinical trials, meta-analyses, and clinical practice guidelines of other organizations concerning cytotoxic oral or IV chemotherapy dosing approaches for overweight or obese patients with cancer, excluding leukemias. Since there have been no prospective randomized studies directly comparing full-weight-based dose selection against other types of dose selection, they had to rely primarily on subgroup analyses and registry data.
Most of the studies concerned breast, ovarian, colon, and lung cancers, the authors said. As little data in the literature addressed dosing for novel agents such as tyrosine kinase inhibitors, immunotherapies such as interleukin-2 or interferon, or monoclonal antibodies, the guideline did not address these agents.
A summary of the guideline (J. Clin. Oncol. 2012 [doi:10.1200/JCO.2011.39.9436]) lists these key recommendations:
• Actual body weight should be used to select cytotoxic chemotherapy doses, regardless of obesity status. There is no evidence that either short- or long-term toxicity is increased with this approach.
• Use the same strategy in obese patients as in other patients for dose reductions, taking into account the type and severity of toxicity, any comorbid conditions, and whether the aim of treatment is cure or palliation. There is no evidence that greater dose reductions are needed for obese patients. Also, consider resuming the full-weight-based dose for subsequent chemotherapy cycles, especially if a possible cause of toxicity (such as impaired renal or liver function) has resolved.
• Consider fixed dosing only with select cytotoxic agents for which maximal dosing limits have been established, such as vincristine, carboplatin, or bleomycin.
• Calculate body surface area using any of the standard formulas currently available. There is no evidence to support using one formula over any other.
• Further research is needed into the pharmacokinetics and pharmacogenetics of chemotherapy dosing for obese patients, who have been excluded from many anticancer drug trials.
The guideline also emphasizes that physicians may need to fully discuss this issue with patients and caregivers, stressing that higher doses are needed in obese patients for the chemotherapy to be effective and reassuring them that toxicity is not expected to be any greater at proportionally higher doses.
"Communication with other health care providers is also warranted. Pharmacists and nursing professionals who are accustomed to limiting chemotherapy doses for obese patients should be informed of the existing evidence. IV and oral doses may be prepackaged for patients of normal weight, but appropriate dosing should be delivered, regardless of doses contained within a given vial. Arbitrary capping based on drug procurement is unacceptable (e.g., 1 vs. 1.5 vials)," the guideline stated.
Clinicians also should be aware that since rates of obesity are higher in black patients, Hispanic patients, and patients of lower socioeconomic status, these groups are harmed the most by underdosing and may benefit the most when full-weight-based dosing is adopted.
"This guideline should ease fears about administering chemotherapy based on actual body weight to otherwise healthy obese patients with cancer," Dr. Gary H. Lyman, cochair of the expert panel that drafted the guideline, said in a press statement.