Given this finding, researchers indicated that further research is crucial to evaluate and address the source of this survival disparity.
“Our findings make it clear that more research is needed to understand factors behind these racial disparities,” first author Hannah Abraham, a graduate student in the University of Michigan (U-M) Cancer Biology program, said in a press release.2 “These factors might include awareness about the signs and symptoms of IBC among Black patients, biological and genetic differences, delays in diagnosis and treatment, the standard of care patients receive, including follow-up and survivorship care, and environmental factors.”
Using the SEER*Stat software version 8.3.5, the investigators extracted a case list of patients with IBC from the November 2017 submission of SEER 18 registries for all cases diagnosed between 1973 and 2015. Importantly, this analysis was unique in that not only were patients who had a diagnosis of IBC based on pathology reports included in the study, but also those with clinical symptoms consistent with IBC. In total, 29,718 patients with IBC were identified and included in the analysis.
The overall incidence of IBC from 1973 to 2015 was found to be 2.76 (range, 2.73-2.79) cases per 100,000 people, with white patients having an incidence rate of 2.63 (range, 2.60-2.67), black patients having an incidence rate of 4.52 (range, 4.39-4.65), and patients of other race having an incidence rate of 1.84 (range, 1.76-1.93). Moreover, the IBC relative 5-year survival rate was found to be 40.5% (range, 39.0%-42.0%) overall, and then 42.5% (range, 40.7%-44.3%) and 29.9% (range, 26.6%-33.3%) for white and Black patients, respectively.
“We found that in these additional patients, the incidence rates by race were consistent with previously reported trends. This gave us confidence that our method was uncovering additional cases that had gone underreported in the past or were possibly misclassified in previous analyses,” senior author Sofia Merajver, MD, PhD, director of the Breast and Ovarian Cancer Risk and Evaluation Program at the U-M Rogel Cancer Center, said in the release. “So therefore, we believe our study is able to offer the most comprehensive assessment of incidence and survival rates of IBC to date.”
Even further, researchers found that patients diagnosed between 1978-1982 have a mean survival time of 62.3 (range, 52.0-72.6) months, while those diagnosed between 2008–2012 have mean survival time of 99.4 (range, 96.4-102.4) months. However, there was no significant difference revealed in survival time between T4D patients and patients with other T staging and extent of disease coding consistent with clinical IBC presentation.
Importantly though, the calculations of IBC mean survival months may be somewhat obscured due to the wide confidence intervals that result from the multiple imputations performed in order to conservatively estimate the survival of patients who had been diagnosed too recently to have more than 60 accrued months of post-diagnosis survival. With consideration to this limitation, the researchers indicated that a less conservative imputation method would still accurately estimate the survival of censored patients, and a larger cohort of patients over a longer time period would also provide a more accurate idea of IBC survival differences between races.
“This would be especially helpful in comparing patients of non-white and non-black race (Asian, Pacific Islander, Native American, etc.), as the relatively low numbers of these patients compelled us to exclude them from the mean survival months analysis,” the authors explained. “However, our work here comprises the largest US cohort on which IBC survival has ever been reported.”