The Laron Syndrome is a condition caused by genetic mutations that make receptors insensitive to Growth Hormone (GH). People with Laron Syndrome therefore are very short in stature, usually shorter than 1.2 meters. And they are almost completely immune to cancer and diabetes, and maybe some other forms of aging-related diseases. Literature (more) suggests that people with smaller body height generally tend to live longer (although others suggest the opposite for women). There is also extensive literature about the rate-of-living theory (the idea that the longevity of an organism is strongly linked to its metabolic rate (although that may also be largely due to statistical artifacts)).
Growth Hormone has anabolic effects, induces growth and increases the metabolic rate of tissue. People with Laron Syndrome seem to fit well into a picture that links growth rates and rates of cancerous mutations and accordingly have a higher life expectancy. Actual quote from Wikipedia: “People with Laron syndrome have strikingly low rates of cancer and diabetes, although they appear to be at increased risk of accidental death due to their stature.”
This article by the New York Times about an Ecuadorian tribe with a high prevalence of Laron Syndrome gives a very entertaining overview of the subject.