The correlation between rates of cancer and autism: an exploratory ecological investigation

Abstract

Background: Autism is associated with high rates of genomic aberrations, including chromosomal rearrangements and de novo copy-number variations. These observations are reminiscent of cancer, a disease where genomic rearrangements also play a role. We undertook a correlative epidemiological study to explore the possibility that shared risk factors might exist for autism and specific types of cancer.

Methodology/principal findings: To determine if significant correlations exist between the prevalence of autism and the incidence of cancer, we obtained and analyzed state-wide data reported by age and gender throughout the United States. Autism data were obtained from the U.S. Department of Education via the Individuals with Disabilities Education Act (IDEA) (2000-2007, reported annually by age group) and cancer incidence data were obtained from the Centers for Disease Control and Prevention (CDC) (1999-2005). IDEA data were further subdivided depending on the method used to diagnose autism (DSM IV or the Code of Federal Regulations, using strict or expanded criteria). Spearman rank correlations were calculated for all possible pairwise combinations of annual autism rates and the incidence of specific cancers. Following this, Bonferroni's correction was applied to significance values. Two independent methods for determining an overall combined p-value based on dependent correlations were obtained for each set of calculations. High correlations were found between autism rates and the incidence of in situ breast cancer (p < or = 10(-10), modified inverse chi square, n = 16) using data from states that adhere strictly to the Code of Federal Regulations for diagnosing autism. By contrast, few significant correlations were observed between autism prevalence and the incidence of 23 other female and 22 male cancers.

Conclusions: These findings suggest that there may be an association between autism and specific forms of cancer.

Figure 1. Spearman rank correlations between annual cancer incidence and autism prevalence.

Pairwise correlations were conducted between the annual incidence of adult cancers (all cancers combined) and the prevalence of autism. For each age group, 56 possible pairwise correlations depending on year were determined. For each year that state cancer incidence (from the CDC) and autism prevalence (from the IDEA) were reported, a two-tailed Spearman Rank correlation coefficient was determined. Significance was adjusted using Bonferroni's correction and shaded as indicated to facilitate visual inspection of the results. The CDC consolidates 24 anatomic sites for all female cancers and 22 anatomic sites for all male cancers.

Figure 2. Autism diagnostic criteria used by states.

The number and identity (by postal state abbreviation) of states that adhere to strict wording in the CFR (CFR only) or expanded criteria (CFR expanded) to diagnose autism are indicated. The diagnosis of autism by CFR is included within the DSM-IV-TR definition, and those states that use the DSM-IV-TR theme are shown (DSM IV autism). States that expand their criteria to include autism spectrum disorder (ASD) represent the fourth criteria used (DSM IV expanded (ASD)).