Biologists: Elephants possess cancer resistance despite large size and long life

The risk of developing cancer usually increases with body size and lifespan in mammals, but elephants and some other animals are an exception. 

This finding is the subject of a study by biologists Juan Manuel Vasquez and Vincent Lynch, published in the journal eLife on Jan. 29. Lynch is an assistant professor at the University of Buffalo in New York, and Vasquez is a post-doctoral researcher at the University of California, Berkeley.

In most animals, the risk of cancer increases in proportion to the total number of cells and cell divisions. But in elephants researchers found a "unique repertoire of tumor suppressor genes." The study showed that additional tumor-suppressor genes help these mammals sustain a large size by decreasing their cancer risk.

The researchers predicted that the additional tumor suppressor genes might be restricted to the larger

Proboscideans species, which are said to have arisen relatively recently from the smaller-bodied

Afrotherians species. The researchers wanted to know whether the tumor-suppressor genes were present in the clade of smaller-bodied species or only in species with the body size expansion. Elephants belong to the Afrotherian group of mammals, which includes mostly small-bodied mammals.

Unexpectedly, researchers found that both lineages of Afrotherian and Proboscideans had increased tumor-suppressor pathways.

"These data suggest that duplication of tumor-suppressor genes is pervasive in Afrotherias and preceded the evolution of species with exceptionally large body size," they write. Further, the researchers say, "the duplication of genes in tumor-suppressor pathways occurred at various points throughout the evolution of Afrotheria, regardless of body size."

However, the Proboscidean lineage had a unique group of pathways that may explain some of the unique cancer protection mechanisms. The researchers suggest that the increase in 12 specific pathways related to cancer may have contributed to "the evolution of large bodies and reduced cancer risk, but that these processes were not necessarily coincident." 

Elephants have a 100- to 100 million-fold reduction in cancer risk that is usually associated with large body size, the researchers note. 

“By determining how big, long-lived species evolved better ways to suppress cancer we can learn something new about how evolution works and hopefully find ways to use that knowledge to inspire new cancer treatments,” co-author Vasquez stated in a University of Buffalo news release on the study.