Observing micopapillary thyroid cancers.

M icropapillary thyroid carcinoma (MPC) is extraordinarily prevalent in the population. Autopsy studies demonstrate an MPC prevalence of 25–35% in Finland and Japan; 10–15% in Canada, Poland, and Colombia; and 5–13% in the United States in adults dying of unrelated causes (1–6). Interestingly, neither the size of the MPC nor the likelihood of finding MPC at autopsy in adults is related to age or sex (2,3,6–11). Until recently, such cancers were considered occult, but high-resolution imaging and aggressive use of fine-needle aspiration have resulted in an epidemic of these small tumors. In the 1960s, only 5% of thyroid surgery was being done for MPC; this increased to 22% by the 1990s (12), and is now approaching 50% of thyroid surgeries at some centers (13–15). And yet, this represents only the tip of the iceberg. If we use 6% as a conservative estimate of the prevalence of MPC in the United States, one would predict over 18 million patients with disease. Yet, the SEER database reports a U.S. prevalence of only half a million cases of all types and sizes of thyroid cancer (http://seer.cancer.gov/statfacts/html/thyro.html). Thus, to date, we have identified less than 3% of the patients with these small tumors. Unless we change our approach to this disease, papillary cancer will continue to be one of the fastest growing malignancies worldwide for many more years.