Studies show that as many as 40 percent of obese patients receive limited chemotherapy doses that are not based on actual body weight, most likely due to concerns about side effects and long-standing practice patterns. ASCO’s new guideline addresses these concerns, stating that clinical trials have clearly demonstrated that weight-based dosing maximizes the effectiveness of treatment for obese patients without raising the risk of side effects.
“This guideline should ease fears about administering chemotherapy based on actual body weight to otherwise healthy obese patients with cancer,” said Gary H. Lyman, MD, MPH, Co-Chair of the ASCO Expert Panel that drafted the guideline, and Professor of Medicine in the Division of Medical Oncology at the Duke Cancer Institutes. “While a chemotherapy dose for an obese patient may be larger than some physicians are accustomed to, they can rest assured that the risk of toxicity associated with chemotherapy dosing based on actual body weight is no greater in obese patients than in non-obese patients with cancer.”
Optimal chemotherapy dosing, established through clinical trials, is generally calculated using a patient’s body surface area (BSA), which takes into account body weight and height. But in practice, some obese patients with cancer receive sub-optimal doses that are calculated based on an “adjusted ideal weight,” which is generally a compromise between a patient’s actual weight and his or her ideal body weight. Inadequate doses of chemotherapy can reduce the effectiveness of treatment, and may explain why obese patients with certain cancers, including breast cancer, have a higher risk of recurrence and death than non-obese patients.
“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,” said Jennifer Griggs, MD, MPH, Co-Chair of the ASCO guideline Expert Panel, and Associate Professor in the departments of Internal Medicine and Health Management & Policy at the University of Michigan (UM), as well as Director of the Breast Cancer Survivorship Program at the UM Comprehensive Cancer Center. “But for obese patients to fully benefit from today’s effective therapies, they need to receive the full, appropriate dose of these medicines.”
To develop the guidelines, an ASCO Expert Panel conducted a formal systematic review of medical literature that was published between 1966 and 2010 on chemotherapy dosing in obese or overweight individuals. Based on World Health Organization criteria, “overweight” people are those who have a body mass index (BMI) of 25-29.9 kg/m2, “obese” individuals are those with a BMI of 30 kg/m2 or more, and “morbidly obese” are individuals with a BMI over 40 kg/m2.
Based on this review of evidence, the guideline specifically recommends the following:
- Actual body weight should be used when selecting cytotoxic chemotherapy (intravenous and oral) doses for all patients, regardless of obesity status: Providing the full dose is particularly important in patients for whom the goal of treatment is cure. There is no evidence that short- or long-term toxicity is increased among obese patients receiving full weight-based chemotherapy doses.
- For morbidly obese patients, full weight-based dosing is recommended: But as for all patients, physicians should consider comorbidities (e.g. heart, kidney, or lung problems) when selecting the chemotherapy dose and should monitor toxicities closely. Data are limited regarding optimal dose selection for morbidly obese patients with cancer.
- Dose reduction for side effects should be made consistently for all patients: Physicians should follow the same guidelines for scaling back the chemotherapy doses in obese patients with severe side effects as they would with non-obese patients.
- Physicians should adhere to established dosing limits on several chemotherapy drugs: These include established maximum doses for vincristine, because of the risk of nerve damage, and bleomycin, because of the risk of lung scarring. Another exception is carboplatin, which should be dosed based on kidney function.
- Additional research needed: The guideline also recommends areas where future research is needed.Most important, studies are needed to better assess how obesity affects the metabolism of newer chemotherapy agents.
The guideline also provides guidance to physicians about communicating with their patients, and with nurses and pharmacists, about the implications of these recommendations on day-to-day practice, including potential cost implications for patients and health insurers.
More information on the new guideline and clinical tools and resources can be found at: www.asco.org/guidelines/wbd.
The American Society of Clinical Oncology (ASCO) is the world’s leading professional organization representing physicians who care for people with cancer. With more than 30,000 members, ASCO is committed to improving cancer care through scientific meetings, educational programs and peer-reviewed journals. ASCO is supported by its affiliate organization, the Conquer Cancer Foundation, which funds ground-breaking research and programs that make a tangible difference in the lives of people with cancer. For ASCO information and resources, visit www.asco.org. Patient-oriented cancer information is available at www.cancer.net.