From Mary Shomon,
Your Guide to Thyroid Disease.
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Research published in the May 2006 issue of the Journal of Clinical Endocrinology & Metabolism has demonstrated that thyroid cancer patients face increased risk of developing second primary cancer.

In this large review study, almost 40,000 people who had primary thyroid cancer were evaluated for up to 25 years, to assess development of second primary cancer. Almost 2000 cases of thyroid cancer, diagnosed after another primary cancer, were also evaluated.

The researcher determined that there were significantly elevated risks for many specific cancers in thyroid cancer patients. Specifically, thyroid cancer patients face a 30% increased risk of second primary cancer, when compared to the general population. It is important to note that these are not metastases -- a spread -- of the initial thyroid cancer -- but instead, appearance of an entirely new cancer.

According to the researchers, thyroid cancer patients faced significantly elevated risks for many specific cancers, including cancers of the following:

• salivary gland
• pharynx
• stomach
• small intestine
• colon
• rectum
• bone
• soft tissue sarcoma
• non-melanoma skin
• female breast
• prostate
• kidney
• brain
• adrenal gland
• non-Hodgkin's lymphoma
• leukemia
• parathryoid gland

The first year after diagnosis is the period during which the risks were highest for non-melanoma skin cancer, prostate cancer, kidney cancer, adrenal gland cancer, and non-Hodgkin's lymphoma. For the other cancers, risk went up after time.

Thyroid cancer risk is also significantly elevated after a number of types of cancer. For people with certain other types of cancer, the risk of developing primary thyroid cancer is also increased. Specifically, those at greatest risk are people who have had cancer of the salivary gland, esophagus, stomach, colon, rectum, liver, pancrease, larynx, lung, bone, soft tissue sarcoma, melanoma, non-melanoma skin, female breast, cervical, uterine, ovarian, testicular, kidney, brain, adrenal, Hodgkin's disease, non-Hodgkin's lymphoma or leukemia.

There is no definitive explanation for the increased risks. In thyroid cancer patients specifically, experts theorize that the use of radioactive iodine -- itself a carcinogenic treatment -- may in part explain the inecreased risk of other cancer. But the experts believe that the carcinogenic effects of the therapy can't explain all of the increased risk .

The experts have several other theories:

• there is a shared genetic risk factor among the various cancers
• there is a shared envionmental risk factor among the various cancers
• there is a shared hormonal risk factor among the various cancers
• various potentially carcinogenic therapies cause the second cancers

Recommendations

1. Physicians who are overseeing the health of patients with primary thyroid cancer should be aware of the risk of second primary cancers in their patients.
2. Physicians who treat other cancer patients should remain aware of the potential for thyroid cancer in their patients.
3. Patients who have had thyroid cancer should make their physicians aware of their medical history, and personally remain aware of their own increased risk of other cancers.

Mary Shomon, About.com's Thyroid Guide since 1997, is a nationally-known patient advocate and best-selling author of 10 books on health, including "The Thyroid Diet: Manage Your Metabolism for Lasting Weight Loss," "Living Well With Hypothyroidism: What Your Doctor Doesn't Tell You...That You Need to Know," "Living Well With Graves' Disease and Hyperthyroidism," "Living Well With Autoimmune Disease," "Living Well With Chronic Fatigue Syndrome and Fibromyalgia," and the "Thyroid Guide to Fertility, Pregnancy and Breastfeeding Success." Click here for more information on Mary Shomon.

Source: Sandeep, Thekkepat C. et. al. "Second Primary Cancers in Thyroid Cancer Patients: A Multinational Record Linkage Study, J Clin Endocrinol Metab 2006 91: 1819-1825; first published February 14 2006 as doi:10.1210/jc.2005-2009