Evaluating Overall Survival in Women with Breast Cancer and Diabetes

Many factors contribute to breast cancer survival inequalities. Yet, because few clinical trials and population-based studies have included underserved racial and ethnic groups as well as low-income populations, the effect of these factors on treatment outcomes is poorly understood.

The Southern Community Cohort Study (SCCS) is a prospective cohort study of underserved, low-income adults with high representation of black participants, which provides a rare opportunity to understand disparities in cancer outcomes. This current study is important because a previous study using SCCS data found no evidence of increased breast cancer risk among women with diabetes in this population. The specific goal of this study is to evaluate whether there is a link between diabetes and overall survival (OS) in women with breast cancer in the SCCS.

The SCCS enrolled approximately 86,000 participants aged 40 to 79 years from 12 southeastern states between 2002 and 2009. Eighty-six percent of these patients were enrolled at community health centers.

Lucy B. Spalluto, MD, Associate Professor, Radiology & Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, and colleagues looked at women diagnosed with incident localized breast cancers who were identified through annual cohort linkage with 12 state cancer registries. From baseline surveys, they gathered demographic information, including participant age at breast cancer diagnosis, patient self-reported history of diabetes (patient answered yes to “has a doctor ever told you that you have diabetes”), body mass index, race, household income, and insurance coverage. State cancer registries provided information about cancer type and stage, while survival data were obtained from death registries. Survival time was defined as the number of months between initial breast cancer diagnosis and death from any cause.

The investigators examined the association between diabetes and OS. Furthermore, they evaluated OS and diabetes, adjusting for age, race, body mass index, insurance coverage, cancer subtype and stage, and household income (annual income <$25,000 and ≥$25,000).

A total of 1347 women were diagnosed with breast cancer. Of these, 1016 were diagnosed with localized disease that ranged from stage I to III. The women included in the study were predominantly black (65.6%) and low income (annual income <$25,000; 70.8%). Approximately 28.8% were privately insured, and nearly two-thirds of participants were covered by government insurance (Medicaid, 23.3%; Medicare, 43.4%).

The average age at diagnosis was 60.7 years. Approximately 25% of the patients had diabetes and 59.6% were obese, with a body mass index of ≥30.

The breast cancer subtypes in this cohort of women included hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative (69.5%); HR-positive, HER2-positive (9.8%); HR-negative, HER2-positive (5.5%); and HR-negative, HER2-negative (15.3%).

Women with diabetes had lower OS (67.4%) compared with women without diabetes (79.8%; P <.0001). Furthermore, the study showed that in women with breast cancer, the diagnosis of diabetes significantly decreased OS, as implicated by a hazard ratio of 1.87.

In a predominantly black, low-income population, with incident localized breast cancer, women with diabetes had decreased OS when compared with those without diabetes. It is important for future studies to explore the impact of other factors, including underlying biological, societal, and socioeconomic factors, that may play a role in survival among women with breast cancer in medically underserved minority populations.