Meeting Abstract

S4-1.5  Jan. 5  Why Don't All Whales Have Cancer? A Novel Hypothesis Resolving Peto's paradox. NAGY, J.D.; Scottsdale Community College john.nagy@sccmail.maricopa.edu

Cancer rates in blue whales (Balaenoptera musculus) should be at least 2000 times higher than in humans simply because blue whales have 2000 times more cells. But the rates appear to be about equal. Three competing hypotheses have been advanced to resolve this paradox--called "Peto's paradox"--in mammals. First, mutation rates may be inversely proportional to body size. Second, malignant cells may enjoy a smaller advantage in larger versus smaller hosts. And third, selection might favor more redundant anticancer mechanisms--like tumor suppressor genes--within the genomes of larger organisms. Here I present a novel hypothesis explaining Peto's paradox. Mathematical models of cancer predict that natural selection will tend to favor malignant cell strains that trade off secondary physiological abilities, like secretion of angiogenesis factors, for growth potential. Such strains then grow as a tumor on their parent tumor, creating a hypertumor that damages or destroys the original neoplasm. Evolutionary models based on these systems suggest that, given enough time, hypertumors will always develop. However, in humans they fail to develop because required mutations do not always arise before the tumor becomes lethal, which occurs when it reaches a mass of one to 2.5 kilograms. However, lethal tumors in blue whales probably weigh at least 2500 pounds. Therefore, they would take at least twice as long to develop in blue whales, providing more time for hypertumors to arise. In this study I test this idea by parameterizing models that originally predicted hypertumors in humans to represent neoplasia in beluga and blue whales. Preliminary results suggest that the hypertumor mechanism may in fact explain Peto's paradox in cetaceans.