Reacción a "Study shows that larger species do develop more cases of cancer, disproving Peto's paradox"

This work is exciting, and I'm glad people are using the data we published!! 

I believe this further supports the most recent existing evidence that has been published of a positive relationship between body mass and neoplasia/cancer prevalence (see: Compton et al, Bulls et al, and Metzger ). I think the most novel contribution is the statistical methods and including the evolutionary history of body size evolution. This work shows accelerated body size evolution is linked to a reduced prevalence of neoplasia and malignancy. 

The findings on Asian elephants are intriguing but they may also be outliers in terms of cancer susceptibility as well. Previous work has shown that Asian elephants are more susceptible to cancer (and other diseases) compared to African elephants, which have very few reported cases of cancer and neoplasia (see Tollis et al). If the results are indeed true, and bigger animals get more cancer, I would have loved to see this validated with cancer mortality data. In other words, even if bigger species get more cancer, does this cancer impact their mortality? 

It's always important to be cautious when interpreting these results due to small sample sizes and these types of statistical methods can have high error rates. In general, we should interpret that these larger species still get less cancer than expected for an animal of their body size. Some species in the dataset have only 20 individuals per necropsy and the breadth (amount of animals) is limited to what is housed in a zoological institution. Adding more species and more individuals per species is going to be a critical next step to validate the relationship between body mass, lifespan and cancer risk. 

The authors admit that "increased rates of body size evolution are associated with the evolution of improved cellular growth control", and mechanisms for this reduced rate in cancer are yet to be discovered!! These mechanisms could be improved cellular growth, better immune function, lower germline mutation rates, or a combination of those factors - depending on what lineage you look at!