Kaiser Permanente study finds tumor characteristics along with socioeconomic factors account for 90% of the survival difference
More aggressive types of uterine cancer that occur more frequently in Black women appear to be the primary reason why Black women are nearly twice as likely to die from uterine cancer as White women, a new Kaiser Permanente study found.
The study, published in the International Journal of Gynecologic Oncology, is the first to analyze disparities in uterine cancer survival among a large group of patients who are all insured and who all have access to the same high-quality care.
“This is one of the largest disparities in cancer survival, and it is critical we do more to understand why,” said lead author Betty Suh-Burgmann, MD, an adjunct investigator with the Kaiser Permanente Division of Research and a gynecologic oncologist with The Permanente Medical Group. “Our study found that the main driver of this disparity is tumor characteristics. More than 70% of the survival gap between Black and White women was explained by the fact that Black patients get more aggressive types of uterine cancer than White women.”
Beyond access to care
The researchers identified 23,529 women diagnosed with uterine cancer between 2005 and 2022 at Kaiser Permanente Northern California or Kaiser Permanente Southern California. There were 12,701 White women and 2,326 Black women within this group who were included in the study. The research team looked at 5 groups of potential risk factors: patient characteristics, how quickly the cancer was diagnosed, tumor characteristics, treatment, and socioeconomic factors. Their analysis showed 2 factors accounted for 90% of the variation in risk of death: tumor characteristics were responsible for 71.3% of the variation and socioeconomic factors responsible for 18.9%.
Tumor characteristics were a key factor, with non-endometrioid uterine cancer — a type of uterine cancer that typically grows and spreads quickly — diagnosed in 51.1% of the Black women compared with 26.5% of the White women. This contributed to advanced disease being present in 36.8% of Black women and 25.6% of White women at diagnosis. In addition, 52.6% of the Black women had grade 3 tumors (the highest grade, with the most abnormal looking cancer cells) compared with 27% of White women. Differences in the presence of other medical conditions, how quickly the cancer was diagnosed, and treatment did not contribute significantly to the survival disparity.
We don’t know why aggressive forms of uterine cancer are more common in Black women, as no genetic cause has been identified, but it is clearly the most significant factor in the disparity we are seeing.
— Betty Suh-Burgmann, MD
“Our findings confirm that within Kaiser Permanente differences in appropriate diagnosis and treatment do not contribute to the survival disparity we see in our patients. Instead, it’s primarily tumor characteristics,” said Suh-Burgmann. “We don’t know why aggressive forms of uterine cancer are more common in Black women, as no genetic cause has been identified, but it is clearly the most significant factor in the disparity we are seeing.”
The second biggest factor in the survival gap was socioeconomic status, which was responsible for nearly 19% of the disparity. This was somewhat surprising, Suh-Burgmann said, because socioeconomic status is typically tied to survival through lack of insurance or patients having more medical conditions. However, all patients in this study were not only insured but had access to the same system, and the presence of other medical conditions was not found to contribute significantly to the disparity.
“We need to learn more about how socioeconomic status influences survival independent of access to care,” said Suh-Burgmann. “There are several potential mechanisms we are aware of. It could relate to less access to healthy food, less opportunity to engage in healthy lifestyle habits, chronic stress, or many other factors associated with social adversity.”
Same incidence, different outcomes
Uterine cancer is the fourth most common type of cancer diagnosed in women in the U.S, and the fifth most common cause of cancer deaths. The American Cancer Society estimates that this year about 68,270 women will be diagnosed with uterine cancer and that about 14,450 women will die from the disease.
The incidence rate of uterine cancer is about the same for Black women and White women — about 28 in every 100,000 women will have this type of cancer diagnosed. But Black women are twice as likely as White women to die of the disease, with 9 in every 100,000 Black women dying compared with 4.6 White women. The 5-year survival rate — a common way to measure cancer deaths — is 63% for Black women and 84% for White women.
Previous studies have found that a higher prevalence of aggressive tumor types in Black women compared to White women is a key factor in the survival difference. But these studies also found survival to be influenced by the presence of other medical conditions, socioeconomic status, insurance status, treatment quality, and how quickly the cancer was diagnosed. Few studies have attempted to assess the importance of various factors relative to each other.
“Our new study is an example of how the research we conduct at Kaiser Permanente can advance our understanding of cancer disparities,” said senior author Julie Schmittdiel, PhD, associate director of Health Care Delivery and Policy and a DOR research scientist. “Conducting this study in a setting where every person has insurance and whose insurance gives them access to the same providers, made it possible for us to account for factors others could not. In doing so, it doesn’t ignore biases that can occur in health care, but it also shows us how much of the disparity is driven by disease characteristics.”
Suh-Burgmann said the study’s conclusions were sobering. “As physicians, we can’t change the kind of cancers people get, or socioeconomic status,” she said. “Reducing the survival gap will depend on developing more effective treatments for these aggressive types of tumors and exploring how we can better support patients to mitigate the negative effects of lower socioeconomic status on health.”
The study was funded by The Kaiser Permanente Garfield Memorial Fund.
Co-authors include Claudia Nau, PhD, and Haoyuan Zhong, of the Department of Research & Evaluation, Kaiser Permanente Southern California; Holly Finertie, MPH, at the Division of Research; Michael Bookman, MD, and Sarah Dolisca, MD, of The Permanente Medical Group; and Devansu Tewari, MD, of The Southern California Permanente Medical Group.
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About the Kaiser Permanente Division of Research
The Kaiser Permanente Division of Research conducts, publishes, and disseminates epidemiologic and health services research to improve the health and medical care of Kaiser Permanente members and society at large. KPDOR seeks to understand the determinants of illness and well-being and to improve the quality and cost-effectiveness of health care. Currently, DOR’s 720-plus staff, including 73 research and staff scientists, are working on nearly 630 epidemiological and health services research projects. For more information, visit divisionofresearch.kp.org.
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