Parathyroid carcinoma in a nonorthotopic supraclavicular location: a 20-year course

Parathyroid carcinoma is a rare cause of primary hyperparathyroidism (PHPT) and is often difficult to distinguish from benign parathyroid disease in its early stages. We describe a nearly 20-year clinical course of recurrent PHPT requiring 4 surgical interventions, ultimately culminating in the diagnosis of parathyroid carcinoma in a nonorthotopic supraclavicular location. The patient was followed continuously at our institution, allowing longitudinal assessment of biochemical, imaging, and histopathological findings. The initial surgery resulted in biochemical remission following removal of a parathyroid adenoma; however, hypercalcemia and elevated intact parathyroid hormone levels recurred over time. Subsequent resections demonstrated parathyroid-type proliferation with increasing Ki-67 index, and the final surgery revealed capsular and venous invasion consistent with carcinoma. Notably, technetium-99 m methoxyisobutylisonitrile uptake became progressively weaker over time and eventually appeared as faint uptake in a nonorthotopic location. These findings may reflect changes in tumor biology over time. Although it remains uncertain whether the supraclavicular lesion represented an ectopic primary carcinoma or metastatic disease from an occult orthotopic lesion, this case highlights the diagnostic challenges of recurrent PHPT and the importance of long-term follow-up, reassessment of atypical locations, and careful interpretation of changing imaging and proliferative indices.