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BMI did not influence outcomes of adjuvant therapy for early-stage breast cancer
Obesity is an independent adverse prognostic factor for death after breast cancer, although the statistical significance was minimal when several other patient characteristics were considered, according to results of a phase 3 study.
The randomized, double blind Breast International Group (BIG) 1-98 trial included postmenopausal women with endocrine-responsive early-stage invasive breast cancer. Researchers compared 5 years of adjuvant monotherapy with tamoxifen or letrozole with sequenced regimens that included 2 years of one followed by 3 years of the other.
Researchers enrolled 8,028 women from 1998 to 2003. They recorded height and weight at randomization to calculate baseline BMI. They classified patients as normal (<25 kg/m2), overweight (25 to <30 kg/m2) and obese (>30 kg/m2).
The current report assessed 4,760 patients who were randomly assigned to 5 years of monotherapy with tamoxifen (n=2378) or letrozole (n=2,382). At randomization, 1,097 of these patients were obese and 1,734 were overweight. The overall median BMI was 26.1 kg/m2 at randomization.
In this study, obese patients had larger tumors (P<0.001) and more positive lymph nodes, and their tumors were more often progesterone receptor-positive (P<0.001).
At a median follow-up of 8.7 years, 17% of patients had died. Patients who were obese had slightly poorer OS (HR=1.19; 95% CI, 0.99-1.44) than patients with a normal BMI, although the difference was not statistically significant. The researchers observed no trend in OS in overweight vs. normal weight patients (HR=1.02; 95% CI, 0.86-1.20).
The results also demonstrated that letrozole was more effective than tamoxifen in reducing DFS events, overall deaths, breast cancer recurrence and distant metastases across all BMI categories.
Perspective
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There is much interest lately in obesity and breast cancer prognosis. This interest is due to multiple factors, not the least of which is that obesity may be a controllable lifestyle variable for many breast cancer survivors. Although some studies have shown decreased survival in women with breast cancer and a high BMI, others have not. Most importantly, few — if any — trials give us hints as to the mechanisms behind such an effect if it truly does exist.
On this background. we now have an analysis by Ewertz and colleagues published in the Journal of Clinical Oncology. The association of BMI with OS was examined in the BIG 1.98 trial, which evaluated adjuvant hormonal therapy in ER-positive, postmenopausal women with early-stage breast cancer. More than 4,700 women were randomly assigned to 5 years of therapy with tamoxifen or 5 years of therapy with letrozole. The study showed that letrozole was superior to tamoxifen in both DFS and OS.
Now, with a median of 8.7 years of follow-up, and 17% of the women in the study having died, the association of BMI with OS was examined. Obese patients (defined as a BMI ≥30 kg/m2) had a slightly poorer OS than patients with a normal BMI. However, a trend toward higher BMI and lower OS was not observed in overweight women (BMI 25 to <30 kg/m2), and none of the trends in any category were statistically significant. There also were no effects of BMI on DFS.
More importantly, there was no impact of BMI on the superiority of letrozole over tamoxifen in either DFS or OS in this analysis. This is important because some have thought that a reason for decreased survival in obese women was because of increased aromatase activity due to an increased number of aromatase-producing fat cells. This result appears to be counter to that hypothesis.
So where are we? Obesity in general is not desirable for overall health, and efforts by all physicians to promote proper diet and weight in all women are necessary. The mechanisms as well as the precise benefits of weight control on breast cancer survival, however, remain to be elucidated.
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