Increased incidence of papillary thyroid microcarcinoma with decreased tumor size of thyroid cancer.

The prevalence of papillary thyroid microcarcinoma (PTMC) in thyroid cancer varies from 20.0% to 42.8% with a mean of 30.0%. Most of these patients have benign clinical courses and receive less aggressive therapeutic procedures in most medical centers. This study retrospectively reviewed 30 years data in one institute and compared it with recent publications to illustrate change in trends and influence of PTMC. Incidental PTMC is usually diagnosed as a postoperative microcarcinoma following thyroidectomy for presumably benign thyroid lesions. Subtotal thyroidectomy or lobectomy without radioactive iodide treatment is sufficient to treat incidental PTMC. In contrast, aggressive surgical treatment with (131)I therapy is indicated for non-incidental PTMC. Those with PTMC in the absence of extra-thyroid invasion diagnosed by postoperative permanent section received follow-up if they had initially received subtotal thyroidectomy. In long-term follow-up studies, cancer-specific mortality for PTMC ranged from 0% to 4%. Most of the mortality cases had distant metastasis at the time of surgery. The clinical course and therapeutic strategies for the non-incidental PTMC patients depend on the TNM stage at the time of diagnosis. One-third of PTMC with clinically aggressive behavior cannot be treated as indolent disease. Invasive tumor markers or larger tumor size are useful to predict tumor recurrence or distant metastasis for PTMC.