Newswise — Patients with micropapillary thyroid cancer—small tumors equal to or less than 1 centimeter—and tumors even smaller, less than 1 millimeter (mm)—are more common and not without a risk as previously thought, according to a new study presented on Fri., Oct. 5, at the 78th Annual Meeting of the American Thyroid Association (ATA) in New York.

This is contrary to the widely perceived belief that small papillary thyroid cancers are clinically insignificant and don't require active treatment. Papillary is the most common type of thyroid cancer, accounting for about 80% of all thyroid cancers.

The findings suggest that the size of the tumor itself may not be the sole determinant for the degree of the cancer's aggressiveness. Small papillary cancer can indeed metastasize or spread to other parts of the body. Ten percent of patients in the study with micropapillary cancer and six percent of those with less than 1 mm cancers had tumors that spread to nearby lymph nodes in the neck.

The study also shows that small papillary thyroid cancer can come back after the initial treatment. In the study, 12 percent of patients with micropapillary cancer who received radioactive iodine treatment after surgery required a second treatment of radioactive iodine, 11-60 months later because the cancer had come back. For those patients with less than 1 mm thyroid cancer, 19 percent of those who received the post-operative radioactive iodine treatment also required a second radioactive iodine treatment.

The standard treatment for papillary thyroid cancer is surgery to remove the thyroid gland (thyroidectomy). If the cancer is large, or has spread to lymph nodes, or if the patient is at a higher risk for cancer to come back, then radioactive iodine ablation therapy is often used to destroy any remaining thyroid cancer cells after surgery. Very frequently, radioactive iodine treatment is not given for small cancers, unless there are some clinical indications or suspicions for more aggressive disease, despite its small size.

Researchers also found that a substantial proportion of patients in their study had micropapillary and less than 1 mm thyroid cancers, suggesting that small papillary cancers are quite common. Close to half (45 percent) of papillary thyroid cancer patients in the study had micropapillary cancer, while over a quarter (26 percent) of these patients had less than 1 mm cancer.

"I hope our study will enhance the understanding of small papillary thyroid cancer, which seems to be increasing in number, yet the natural course or optimum treatment is not well known," said Haruko Akatsu Kuffner, M.D., author of the study and Assistant Professor of medicine, Division of Endocrinology and Metabolism at the University of Pittsburgh in Pittsburgh, Pa.

"We would like to be appropriately aggressive in treating small aggressive cancers. However, it is also important not to be aggressive in managing the majority of these patients with clinically insignificant small cancers. A better understanding of this disease will help us to better risk stratify these patients," added Dr. Kuffner.

This large, retrospective study involved reviewing the records from 1992 to 2004 of 888 papillary thyroid cancer patients with original pathology records including the cancer size available through the use of the University of Pittsburgh Thyroid Cancer Database.

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American Thyroid Association Annual Meeting