– a potentially deadly outcome that can occur as a result of chemotherapy treatment.
The study was presented at the annual meeting of the American Society of Clinical Oncology.
It is known that body mass index can affect breast cancer risk and prognosis, but it is not known if BMI can affect how well endocrine therapy works in a given patient. In the PALLAS clinical trial, Georg Pfeiler, MD, Medical University of Vienna, and colleagues, conducted an analysis of 5,698 patients with early hormone receptor–positive breast cancer receiving endocrine therapy with or without palbociclib. Dr. Pfeiler found that women who are overweight or obese had significantly less frequent and less severe cases of neutropenia. With fewer or less severe cases of neutropenia, there were also fewer interruptions in palbociclib treatment.
“One explanation for the lower discontinuation rates may be that the distributional volume of the drug is higher in overweight and obese patients leading to lower serum drug concentrations. It could also be influenced by differences in pharmacokinetics with respect to hyperinsulinemia,” said Dr. Pfeiler, who leads the Oncological Breast Outpatient Clinic and Bone Health Outpatient Clinic at the Medical University of Vienna.
The PALLAS trial compared the combination of palbociclib and adjuvant endocrine therapy with endocrine therapy alone in 5,698 women with early breast cancer. Patients were categorized according to BMI as underweight (BMI < 18.5 kg/m2), normal weight (BMI 18.5-24.9), overweight (BMI, 25-29.9), and obese (> 30). The investigators analyzed differences in adverse events, time to early discontinuation of palbociclib, and in time to invasive disease-free survival.
At baseline, of 5,698 patients, 68 (1.2%) were underweight, 2,082 (36.5%) were of normal weight, 1,818 (31.9%) were overweight, and, 1,730 (30.4%) were obese. In patients treated with palbociclib, neutropenia was the primary toxicity leading to treatment discontinuation with rates of 21.1% in normal-weight patients, 14.0% of overweight patients, and 5.9% of obese patients, respectively.
Significantly different rates of all-grade neutropenia were observed in normal weight, overweight, and obese participants with regard to total (88.5%, 85.7% and 74.7%), as well as grade 3 (64.1%, 62.0% and 43.9%) and grade 4 neutropenia (7.0%, 3.6% and 2.0%), respectively. The lower frequency and severity of neutropenia observed in overweight and obese patients was associated with a significantly lower treatment discontinuation rate over time when compared with normal-weight patients (overweight vs. normal weight: HR, 0.73; 95% CI 0.63-0.84; P < .0001, and obese vs. normal weight: HR, 0.65; 95% CI, 0.56-0.75; P < .0001). There was, however, despite these observations, no statistically significant improvement in invasive disease survival with the addition of palbociclib to endocrine therapy in any weight category (normal weight: HR, 0.84; 95% CI 0.63-1.12; overweight: HR, 1.10; 95% CI 0.82-1.49; and obese: HR, 0.95; 95% CI, 0.69-1.30).
“This is an early analysis, and should be interpreted with caution, especially with regard to disease outcomes. The findings may reduce concerns over hematologic side effects in the overweight and obese. In the future there may be an important impact if it turns out after longer-term follow-up that palbociclib has been underdosed in the overweight and obese. We may need BMI-adapted dose management,” said Dr. Pfeiler, who is currently working on a longer-term follow-up study of the PALLAS group.
The analysis found no significant correlation between weight and occurrence of invasive disease events.
Dr. Pfeiler disclosed honoraria and grants from Pfizer. The study was funded by Alliance Foundation Trials.