Tumor Size and Presence of Metastatic Disease at Diagnosis are Associated with Disease-Specific Survival in Parathyroid Carcinoma

Background: The incidence of parathyroid carcinoma is reported to be rising. There is minimal data on prognostic variables associated with cancer-specific survival. The objectives of this study were to evaluate the trends in incidence and assess prognostic factors. Methods: A retrospective review of the SEER database between 1973 and 2014 was performed, identifying 520 patients with parathyroid carcinoma. Population-adjusted incidence rates were calculated in 4-year intervals. A Cochrane-Armitage test was performed to analyze changes in trend in incidence, tumor size, and extent of disease. Age, year of diagnosis, race, gender, extent of disease, surgical resection, treatment with radiation, tumor size, and lymph node status were assessed using Mantel-Cox log rank test. Multivariate analysis was performed by Cox regression analysis. Results: The incidence of parathyroid carcinoma has been increasing since 1974 from 2 to 11 cases per 10 million people but has since stabilized at 11 cases per 10 million people since 2001. The increasing incidence was attributed to locoregional disease and tumor size < 3 cm. The presence of metastatic disease [hazard ratio (HR) 111.4, 95% confidence interval (CI) 20.6–601.8, p < 0.0001) and tumor size > 3 cm (HR 5.6, 95% CI 1.5–21.2, p = 0.011] were associated with worse cancer-specific survival by univariate and multivariate analyses. Conclusions: The incidence of parathyroid carcinoma has remained stable over the past decade. Tumor size < 3 cm and regional disease have increased in incidence. Patients with metastatic disease and tumors > 3 cm have worse cancer-specific survival. These findings can be incorporated in the development of a staging system for parathyroid carcinoma.