Does iodine prevent cancer?

Question

I have recently found claims that iodine can prevent cancer. Eg:

• breast cancer
• a variety of cancers
• "especially in breasts, ovaries, uterus, prostate and thyroid gland"

and many more sites. Wikipedia states:

Whether iodine/iodide will be useful... in women with breast cancer has not been determined clinically.

The same section implies a positive correlation between iodine and reducing the risk of stomach cancer.

So can iodine really prevent or at least reduce the risk of some cancers? If so, does that apply to more cancers beyond stomach cancer?

Answer 1

According to Molecular Iodine Induces Caspase-independent Apoptosis in Human Breast Carcinoma Cells Involving the Mitochondria-mediated Pathway The Journal of Biological Chemistry (2006) vol. 281, pages 19762-19771

Molecular iodine (I2) is known to inhibit the induction and promotion of N-methyl-n-nitrosourea-induced mammary carcinogenesis, to regress 7,12-dimethylbenz(a)anthracene-induced breast tumors in rat, and has also been shown to have beneficial effects in fibrocystic human breast disease. Cytotoxicity of iodine on cultured human breast cancer cell lines, namely MCF-7, MDA-MB-231, MDA-MB-453, ZR-75-1, and T-47D, is reported in this communication.