SAN ANTONIO — A high C-peptide level appears to be an independent risk factor for breast cancer recurrence and death—but that doesn't explain the relatively poor prognosis in Hispanic women with the malignancy, Richard N. Baumgartner, Ph.D., said at a breast cancer symposium sponsored by the Cancer Therapy and Research Center.
The incidence of breast cancer among Hispanic women is known to be lower than in non-Hispanic white women. Yet, once they develop the malignancy, their prognosis is markedly worse. The Health, Eating, Activity, and Lifestyle (HEAL) study is an ongoing cohort-based epidemiologic investigation being conducted in New Mexico, Los Angeles, and Seattle in an effort to understand why, explained Dr. Baumgartner of the University of New Mexico, Albuquerque.
His hypothesis was that the ethnic disparity in breast cancer outcome might be due, at least in part, to the increased prevalence of the metabolic syndrome among Hispanics. But this proved not to be the case in his analysis of 124 Hispanic and 370 non-Hispanic, white New Mexican women with invasive breast cancer participating in HEAL.
There were 20 cases of breast cancer recurrence or a new primary cancer and 46 deaths due to breast cancer during 5 years of follow-up; the risk of these bad outcomes was 2.03-fold greater among the Hispanic women.
In the HEAL study population, the presence of insulin resistance and central obesity—key components of the metabolic syndrome—was indeed associated with increased risk of breast cancer recurrence and mortality, but this association proved to be independent of ethnicity.
In a multivariate analysis adjusted for waist to hip ratio, percent body fat, and level of C-peptide—an accepted biomarker for hyperinsulinemia and insulin resistance—Hispanic ethnicity still remained associated with a 2.01-fold increased risk of breast cancer recurrence or death. This observation strongly suggests that the metabolic syndrome doesn't explain the ethnic difference in disease recurrence and survival, Dr. Baumgartner said.
When the multivariate model controlled for ethnicity as well as waist to hip ratio and body fat, patients in the highest quartile for C-peptide had a 2.07-fold increased risk of recurrence and death, while those in the middle two quartiles were at 67% greater risk than those in the lowest quartile.
In a larger group of 616 HEAL study participants, there were no significant differences between Hispanic and non-Hispanic white patients in terms of mammography-screening interval, how the cancer was diagnosed, number of biopsies, or family history.
The two groups didn't differ in terms of disease stage, positive lymph node count, human epidermal growth factor receptor 2 (HER-2) status, or Ki-67 expression. There were few treatment differences between the two groups. But Hispanic patients were significantly more likely to present with large hormone receptor-negative tumors.
The inference is that Hispanic patients may have a different breast cancer phenotype than non-Hispanic whites, according to Dr. Baumgartner.