Papillary microcarcinoma (PMC) is generally considered as a very low risk disease. Therefore the possibility of distant metastasis is very low and the prognosis is excellent. But even with the very low risk, this do not mean that PMC will never have distant metastasis. We report 6 cases of distant metastasis due to PMC who underwent radioiodine therapy (RAI).
From January 2007 to December 2016, initial RAI were performed for distant metastasis in 143 cases. Among the 143 cases, we found that 6 cases of PMC. In the 6 cases, pathology showed that 3 had lymph node metastasis and 3 had multiple lesions in the thyroid, but only in 1 case lymph node metastasis were detected before surgery and none of the multiple lesions were detected on ultrasound. In 2 cases the original lesion could only diagnosed by pathology. 2 cases died due to thyroid cancer.
Because of the low risk of PMC, active surveillance is recommended. In active surveillance, the enlargement of the original lesion is said to be a sign of aggressiveness. Although in our group, the original lesions were still smaller than 10mm in diameter. Lymph node metastasis is also a sign of aggressiveness but 2 out of 3 cases could not be detected by ultrasound. The rate of distant metastasis of PMC is less than 1.0%, and some even claim that there are no incident of death. Despite this claim, 2 out of 6 cases died due to thyroid cancer in our group.
From our result, although the risk of PMC is very low, it could be a cause of death in some cases.