Effects of Pregnancy on Papillary Microcarcinomas of the Thyroid Re-Evaluated in the Entire Patient Series at Kuma Hospital

Background: An active-surveillance clinical trial of low-risk papillary microcarcinoma (PMC) patients has been performed at the authors' institution, Kuma Hospital, since 1993. Favorable oncological results have been reported. During the trial, a few patients were encountered with PMC that showed enlargement during pregnancy, and these cases have been reported. During pregnancy, a large amount of human chorionic gonadotropin (hCG) having weak thyrotropin (TSH) activity is produced, possibly affecting the progression of PMC. This study investigated how pregnancy and delivery influenced the progression of PMC in the entire active surveillance PMC patient series. Methods: From 1993 to 2013, 1841 patients with low-risk PMC chose the active surveillance program. Fifty of the 1549 female PMC patients experienced 51 pregnancies/deliveries. To minimize observer variation, a single specialist sonographer re-evaluated the changes in the size of these 50 patients' PMCs before and after the pregnancies/deliveries. Results: Four patients (8%) showed enlargement of PMC by ≥3 mm; one patient (2%) showed a decrease by ≥3 mm, and the remaining 44 patients (45 events, 90%) showed stable disease. None of the patients had a novel appearance of lymph node metastases during pregnancy. Of the four patients with enlargement, two underwent surgery after delivery, and the other two continued the active surveillance, since their tumors did not grow after the delivery. After delivery, the PMC of one of these four patients remained stable, and another showed a decrease in PMC size. To date, six more PMC patients underwent surgery after delivery for reasons other than disease progression due to pregnancy and delivery: two opted out of active surveillance, two were identified with a nodal metastasis during active surveillance after delivery, one had Graves' disease, and one showed enlargement of nodules of the contralateral lobe. Conclusions: Pregnancy and delivery was associated with an increase in size of PMCs in only 8% of the 51 pregnancies/delivery cases. None of the patients developed nodal metastasis during pregnancy. Thus, a possible future pregnancy does not prevent such patients from undergoing active surveillance, although watchful observation during pregnancy is recommended.