Despite Declines in Incidences, Outcomes in Brain Cancer Remain Suboptimal

Incidence rates of adult brain tumors are decreasing; however, 5-year survival rates remain low, according to a new report by the American Cancer Society.¹

Between 2008 and 2017, the rate of central nervous system tumors decreased by 0.8% annually, for all ages. The trend was driven by adults, with the incidence of brain tumors in children increasing by 0.5% and in adolescents by 0.7% annually over the same period.

Data for the study was collected using the National Cancer Institute's Surveillance, Epidemiology, and End Results program and the Centers for Disease Control and Prevention's National Program of Cancer Registries (NPCR). These 2 databases were combined by the Central Brain Tumor Register of the United States.²

Rates of malignant brain tumors were higher in males, with a rate of 8.3 cases per 100,000 people compared to 6 per 100,000 people. However, nonmalignant rates were higher for females (20.3) than males (12.8). Sex differences for malignant tumors were the largest in patients 45 years of age or older, with the rates for females being 30% lower than in males. However, for nonmalignant tumors, sex differences were greater between 25-29 years of age, with rates being two-fold for women (10.2) compared to men (4.7). This is due to higher pituitary adenoma rates in women of this age group. 

The 5-year survival rate stands at 36%, which is up from 26% in the mid-1970s. The slow progress on increasing survival can mostly be blamed on the lack of advancement in early glioblastoma detection, which accounts for 49% of all malignant brain cancers in the United States. 

Broken down by race, the 5-year overall survival between 2009 to 2015 was the lowest for non-Hispanic White patients at 31% to 48% for Hispanic patients. However, the study notes that it is important to realize that this is in part due to the loss of follow-up for this patient population. The 5- year survival rate for White patients is lower due to the burden of glioblastoma and other diffuse gliomas.

The incidence rates of nonmalignant tumors, which disproportionately affect women and Black patients, are also increasing. This is most likely due to increased awareness and improvements in case findings. Rates for meningioma, which accounts for 54% of all nonmalignant cases in the United States, increased by 0.9% annually between 2008 to 2017. While the 5-year survival rate for nonmalignant tumors stands at 92%, patients often have long-term side effects from the tumor and/or treatment.

The largest survival gains were made by individuals between 20 and 39 years of age, for whom 5-year survival increased from 44% to 73%. Lower gains were seen in older age groups, mostly due to the lack of improvement of glioblastoma survival. For this population, glioblastoma survival increased from 4% for those diagnosed between 1975 and 1977 to 7% for patients diagnosed between 2009 and 2015.

The report also found racial disparities, especially among children. For example, the brain cancer mortality rate is the same in White and Black children. However, the incidence rate is lower in Black children. The Black-White disparity was the largest for children diagnosed during 2009 to 2015 in diffuse astrocytomas (75% versus 86%, respectively) and embryonal tumors (59% versus 67%).

The report also noted environmental factors that contribute to brain tumor risk. Currently, there is only 1 established brain tumor environmental risk factor: exposure to ionizing radiation. This association is strongest for meningioma and glioma in younger patients. Patients who also received cranial radiation as treatment for acute lymphocytic leukemia in youth are also at a higher risk for subsequent brain tumors.

Additionally, hereditary risk factors have been found for certain brain tumors, but this makes up a very small proportion of cases. For example, the study states that certain Mendelian syndromes are associated with an increased risk for familial adenomatous polyposis and Turcot syndrome type 1 and type 2 for medulloblastoma and gliomas. Germline mutations have also been associated with an increased risk of brain tumors for specific histologic types. However, most of these studies were conducted in older European adults, and data are limited for children and other racial/ethnic groups.

“Although the molecular understanding of how brain cancers differ from each other is advancing rapidly, we continue to know little about why these tumors develop in the first place. To facilitate greater understanding, it critical to have access to timely, comprehensive data on occurrence,” said Kimberly D. Miller, MPH of American Cancer Society, in a press release. “This is particularly important to understand the causes of sex, age, and racial/ethnic differences, especially for rarer subtypes and among understudied populations.”

_REFERENCES:

_{1.Report shows adult brain tumor incidence rates are decreasing but 5-year survival rates remain low. News release. American Cancer Society. August 24, 2021. Accessed August 24, 2021. https://bit.ly/3sKKBq8.}

_{2.Miller K, Ostron Q, Kruchko C, et al. Brain and other central nervous system tumor statistics, 2021. CA Cancer J Clin. 2021 Published online ahead of print. doi: 10.3322/caac.21693.}