Enhanced risk of cancer in companion animals as a response to the longevity

Cancer arises from lifetime accumulation of somatic genomic and epigenomic alterations occurring at very low error rates during replication. Long-lived species (e.g., elephants) appear to have evolved mechanisms that slow cancer progression. Recently, improved environments have extended the lifespan of companion dogs and increased the fraction developing cancer, suggesting short-term responses of cancer risk to longevity differ from long-term evolutionary responses. Using a simple multi-step model of cancer in which event rates toward malignancy scale with the genomic replication error rate x, we show that perfect error removal is too costly, leading to evolution of a positive error rate. When the environment suddenly improves (lower noncancer mortality), the relative importance of cancer increases even though age-specific cancer risk is unchanged. Over many generations, x evolves downward, mitigating cancer risk.