Effect of diabetes on survival in myeloma may differ by race: Study

While diabetes is more frequent among Black people than white people, it’s associated with poorer survival outcomes in white people with multiple myeloma, a U.S. study shows.

“We knew from prior studies that patients with multiple myeloma and diabetes have lower survival rates. But what we did not know is how these outcomes differ between races,” Urvi Shah, MD, the study’s first author at Memorial Sloan Kettering Cancer Center, said in a press release from the American Society of Hematology (ASH). “What we did not expect to see here was that diabetes was actually associated with worse survival outcomes among white individuals with myeloma, but not Black individuals.”

The difference may be due to diabetes affecting a greater proportion of younger Black myeloma patients relative to their white counterparts, and younger patients may be more tolerant to treatment, the researchers noted.

The researchers also provided the first mechanistic evidence that diabetes speeds the growth of multiple myeloma in a non-obese mouse model of the disease, further confirming its impact on myeloma.

The findings suggest diabetes “may contribute to the higher incidence of MM [multiple myeloma] in Black patients, and [that] to improve survival in MM, [diabetes] management cannot be ignored,” the researchers wrote in “Prevalence and impact of diabetes on survival of patients with multiple myeloma in different racial groups,” which was published in ASH’s journal Blood Advances.

In the U.S., rates of both multiple myeloma and diabetes are higher in Black populations, though the reasons for these racial differences aren’t well understood. While studies have shown that having diabetes tends to be linked with worse outcomes among myeloma patients, it hasn’t been clear if this effect differs among racial groups, leading the scientists to analyze data from 5,383 multiple myeloma patients. Most (81%) were white, just over half were male, and about two-thirds were older than 65. The median follow-up time was more than four years.

Diabetes associated with higher mortality risk

Overall, 15% of the patients had co-occurring diabetes, but the rate of diabetes was about twice as high in Black than white patients (25% vs. 12%). Compared with white patients with diabetes, Black patients tended to be younger and were less frequently obese.

Statistical models were developed to compare the risk of mortality in patients with or without diabetes. In the overall population, diabetes was associated with a significantly higher risk of death, by about 17%.

For white patients, the risk of death also was significantly higher among those with diabetes, by about 44%. However, in Black patients, having diabetes was associated only with a slightly increased risk of death that didn’t reach statistical significance, meaning the difference could be due to chance.

Researchers called this racial difference in survival among patients with and without diabetes an unexpected finding.

The risk of death was higher with older age in patients of all races. Given that diabetes was nearly twice as common among younger Black patients, ages 45-60, relative to white patients 60 and older (20.2% vs.14.2%), the researchers suggested this may explain why diabetes wasn’t significantly linked to mortality in Black patients, who may have “had better tolerance to MM treatments, and their potential complications, than the older white” patients with diabetes.

Rates of death tended to be slightly lower in white patients than Black patients irrespective of diabetes, further analyses showed. The difference wasn’t statistically significant, however.

A higher body mass index (BMI), generally indicating overweight and obesity, was associated with a significantly lower risk of death in Black but not white patients. Being male was also linked to a significantly increased risk of death in Black patients. BMI is a ratio of weight to height.

Testing diabetes in myeloma mouse model

The researchers also conducted experiments in a mouse model of myeloma with or without diabetes and found cancerous myeloma cells grew significantly faster in non-obese mice with diabetes. This may be because these mice had higher insulin levels, which activated growth pathways in the cancer cells.

“The higher prevalence of [diabetes] in Black patients, our preclinical data from mouse models, and the known increased risk for MM in [people with diabetes] suggests that [diabetes] may be a risk factor contributing to the increased development of MM in Black individuals compared to White individuals,” wrote the researchers, who noted the data suggest that effectively treating diabetes may improve outcomes for myeloma patients who have the condition.

“In my own practice, I work with many patients with both multiple myeloma and diabetes,” said Shah, who noted outcomes might improve by treating diabetes, instead of just treating the multiple myeloma with rounds of chemotherapy. “While drugs are important, as oncologists, we need to also look at [simultaneous health conditions] and modifiable risk factors to improve patient survival outcomes.”