A Retrospective Case-control Study of Tumor Characteristics of Coexistent Papillary Thyroid Carcinoma Diagnosed in Surgically Treated Patients for Secondary Hyperparathyroidism: Higher Incidence and More Often Occult Papillary Thyroid Carcinoma

Abstract Background :Coexistence of primary hyperparathyroidism (PHPT) and PTC is common and may be associative with more aggressive papillary thyroid carcinoma (PTC) for higher rates of extrathyroidal extension and multicentricity. However, it remains unclear whether secondary hyperparathyroidism (SHPT) accounts for more invasive PTC in terms of morbidity, tumor pathological characteristics and prognosis . The aim of this study was to evaluate the rate and tumor characteristics of PTC in patients operated for secondary hyperparathyroidism (SHPT).Methods:A total of 531 patients with PTC who underwent surgery were evaluated retrospectively from January 2013 to December 2018 in the first affiliated hospital of the Zhejiang University. Patient demographics, operative and postoperative outcomes were recorded and analyzed. Among them, 34 patients of co-occurrence of secondary hyperparathyroidism and papillary thyroid carcinoma (PTC+SHPT) were enrolled. Control subjects were derived through 1:4 matching for age, sex and gender pathological subtype. 34 patients of co-occurrence of secondary hyperparathyroidism and papillary thyroid carcinoma (PTC+SHPT) were selected as control group after matching 1:4 for age, gender and pathological subtype.Results:There were 34 patienst coexisting with PTC+SHPT among the 531 surgery patients of SHPT(6.4%). Mean tumor diameter of group PTC+SHPT was smaller than that in group PTC (5.57mm vs 9.00mm, p=0.000). The proportion of papillary thyroid microcarcinoma(PTMC，means PTC with a diameter smaller than 10 mm) in group PTC+SHPT were significantly higher than that in group PTC [29 (85.29%) vs 86 (63.24%), P=0.014]. There were no statistically significant difference among the tumor multicentricity [15 (44.12%) vs 39 (28.68%), P=0.066], tumor bilaterally [9(26.47%) vs29(21.32%), P=0.499]，tumor extrathyroidal extension [2(5.88%) vs19 (13.97%), P=0.255] and lymph node metastasises rate [12 (35.29%) vs 49 (36.03%), P=1.000]. We found differences between group PTC+SHPT and group PTC patients with respect to contralateral thyroidectomy [10 (29.41%) vs 70(51.47%), P=0.023] and lymph node dissection [22 (64.71%) vs 125(91.91%), P=0.000].There was no significant difference between group PTC+SHPT and group PTC in prognostic staging [33 (97.06%) vs 122 (89.71%), P=0.309] and recurrence [mean follow-up time 36 months vs 39 months, P=0.33].Conclusions: The prevalence of PTC is higher in patients with SHPT than in the general population. Compared with PTC in the general population, most of PTC with SHPT are occult thyroid carcinoma and present no significant difference in tumor multicentricity, tumor bilaterally,tumor extrathyroidal extension, lymph node metastasises and prognostic staging. It’s necessary for surgeons to make more adequate preoperative prediction and do more careful examination during the surgery in case of missing the coexistence of PTC in SHPT patients.