Background: Atypical parathyroid adenoma (APA) is a rare entity, sharing clinical symptoms like solid palpable mass in the neck, laboratory changes with very high serum calcium and parathyroid hormone levels, and some histopathological features with parathyroid carcinomas (PC). However, clinical behavior of APA seems to comply with benign parathyroid tumors (PA). There is some evidence that loss of the membranous staining pattern of E-Cadherin (E-Cad) suggests a key role of epithelial mesenchymal transition in the tumorigenesis of PC. Thus, the aim of this study was to compare clinical and surgical characteristics and immunohistochemical expression of E-Cad in APA, PC, and PA.
Methods: Data of patients who underwent surgery for primary hyperparathyroidism (pHPT) between 1985 and 2010 were retrospectively evaluated. All data were analyzed with special regard to distinctive criteria of APA, including trabecular growth, broad fibrous bands, nuclear atypia, mitosis, pseudocapsular invasion or strong adherence to the surrounding tissue, and potential invasive growth of a grossly altered and enlarged parathyroid gland. In addition, laboratory and clinical data were evaluated and additional immunohistochemical staining with E-Cad was performed in suspicious APA patients with available tissue.
Results: In 68 patients (39 female, 29 male), the parathyroid tumor was suspicious for APA. In 46 patients, a bilateral cervical exploration was performed. 15 patients underwent an en bloc resection including a hemithyroidectomy and lymphonodular dissection of the ipsilateral central compartment due to the malignant macroscopic aspect of the parathyroid. In seven patients, a focused parathyroid resection was done. The available parathyroid tissue of 38 APA patients was immunopositive for membranous E-Cad staining. During follow-up, only one patient with a successful initial surgery suffered from recurrent pHPT due to another solitary PA 10 years after initial surgery but without evidence of malignancy.
Conclusions: In contrast to PC, parathyroid tumors suspicious for APA are characterized by a strong membranous E-Cad staining and, like PA, by a benign clinical course.