Genetic changes in thyroid cancer block vitamin D3 absorption in tumor cells

A recent letter to the editor of the journal Thyroid commented on the apparent connection between papillary thyroid cancer (PTC) and the overexpression of the CYP24A1 gene, which codes for enzymes that deactivate vitamin D3.

The short article, written by a dozen physicians at Semmelweis University in Budapest, noted that if the CYP24A1 gene is overused by thyroid cells, their consequent insensitivity to vitamin D3 could predispose them to unchecked growth.

Vitamin D3 is one of two forms of the nutrient that the human body can use. The skin naturally synthesizes this type of the vitamin after direct exposure to sunlight or ultraviolet rays. Certain foods contain vitamin D3, such as beef or fish livers, egg yolks, cheese, mushrooms and fortified milk, the National Institutes of Health reports.

Numerous studies have shown that the active metabolite of this vitamin, known as 1,25-dihydroxyvitamin D3 (1,25-D3) prevents tumor cell growth and encourages programmed cell death in a number of different forms of cancer.

In the new letter, the Hungarian research team noted that overexpression of the CYP24A1 gene can be found in nearly all forms of PTC. When this stretch of DNA is repeatedly activated in thyroid cells, it produces excess amounts of enzymes that deactivate 1,25-D3.

The letter's authors said that while the connection between the body's levels of vitamin D3 and PTC is still unclear, overactivation of the CYP24A1 gene inhibits the cancer-slowing properties of both naturally occurring 1,25-D3 and calcitriol, a pharmacological, hormonally active form of the nutrient that increases calcium absorption.

A 2002 study in the American Journal of Pathology previously established that vitamin D-like molecules can inhibit the growth of thyroid tumors.

The A. P. John Institute for Cancer Research states that consuming vitamin D can inhibit the activity of enzymes called kinases, which are essential for PTC growth.

At least 70 percent of Americans diagnosed with thyroid cancer have PTC, according to the Columbia University Department of Surgery.