Thyroid cancer raises risk of second cancer

NEW YORK, May 27 (Reuters) After surviving cancer of the thyroid, the risk of a second different cancer is elevated by about 30 per cent, according to results of a new study. Conversely, many cancers are associated with increased risk of subsequent thyroid cancer.

Dr Mark W J Strachan, from Western General Hospital in Edinburgh, UK, and colleagues note that the increased rate and improved prognosis of thyroid cancer, as well as its greater occurrence in children, suggests that other cancers are increasingly likely.

To test this theory, they combined data from 13 population-based cancer registries that have been in operation for at least 25 years in Europe, Canada, Australia, and Singapore. Their findings appear in the Journal of Clinical Endocrinology and Metabolism.

There were 39,002 people with thyroid cancer, among whom 74 per cent were female and 57 per cent were younger than 56 years.

During several years of follow-up, 2821 other cancers were diagnosed.

Many of the second cancers are diagnosed within the first year, primarily skin, prostate, kidney, adrenal gland, and non-Hodgkin's lymphoma. For some other cancers, such as those of the small intestine, colon, rectum, and breast, the risk increased with duration of follow-up.

The authors also found that 1990 cases of thyroid cancer were diagnosed after another cancer occurred. In this case, the risk of thyroid cancer was not associated with age, gender or calendar period of diagnosis.

The only cancers not significantly associated with increased risk of thyroid cancer were those of the lips, mouth, pharynx, gallbladder, some female genitals, prostate, and bladder. For most of the cancer types, the risk of thyroid cancer was highest during the 12 months following the diagnosis of the first.

Strachan's group notes that two-way associations between cancers raise the possibility of shared genetic, hormonal or environmental risk factors or the use of potentially cancer-causing therapies for both cancers.

The authors recommend that doctors be on the lookout for other cancers in patients who've been diagnosed with thyroid cancer and vice versa.

REUTERS DKS BD0912