A tumor on the pituitary gland in the brain can sometimes lead to a condition known as gigantism or giantism. This affliction causes excessive growth generally significantly above most others of the same ancestry, age, race and sex.
The increased infusion of growth hormone generally through childhood from the pituitary gland can cause a person's height to skyrocket over nine feet.
Gigantism isn't simply given to someone who is just tall. There are tests that can be run to test for high levels of growth hormone.
Increased growth hormone after puberty can lead to a condition called acromegaly. This condition causes a number of disfigurements as well as possibly leading to early death.