LAUSR

Abstract Parathyroid gland malignancies are rare, the most common of which is primary parathyroid carcinoma. Metastatic disease to the parathyroid gland is not well described in the literature. Based on autopsy studies, metastatic involvement of the parathyroid gland among known cancer patients is 0.2-11.9%. Literature suggests a predilection for tumors to spread to endocrine organs possibly due to the plentiful blood supply. We present the unique case of a patient presenting with primary hyperparathyroidism, which ultimately lead to a diagnosis of stage IV breast cancer. A 77-year-old female was referred to endocrinology for hypercalcemia. Her calcium level was elevated at 10.5 mg/dL (normal 8.5-10.1 mg/dL) with an intact PTH of 171.3 pg/mL (normal 14.0-72.0 pg/mL), consistent with primary hyperparathyroidism. She was symptomatic with polyuria, polydipsia, constipation, weakness, and recent 25lb weight loss that she attributed to decreased appetite. The patient denied taking calcium supplements, personal history of kidney stones, or family history of MEN syndromes. Her BMI was 23 kg/m2 and her physical exam was otherwise unremarkable. Renal ultrasound was negative for nephrolithiasis. DEXA scan confirmed osteoporosis of the left hip (T score -3.4), left femoral neck (T score -3.5), and left forearm (T score -5.4) as well as osteopenia of the lumber spine (T score -1.8). A Sestamibi scan noted persistent focal activity localizing to a 1.3 x 1.2cm soft tissue density nodule posterior to right thyroid lobe, consistent with a parathyroid adenoma. She underwent a right superior and inferior parathyroidectomy based on intraoperative appearance of the glands. Pathology report detailed the right inferior parathyroid gland was normocellular parathyroid tissue, however the right superior parathyroid gland, weighing 1030mg, revealed hypercellular parathyroid tissue with a 0.5cm deposit of metastatic carcinoma consistent with breast primary. Mammogram was negative for breast malignancy. Subsequently, PET scan revealed metabolically active metastases throughout pleura, thorax, chest wall, bones, and right colon. The patient was diagnosed with stage IV hormone receptor positive and Her-2/neu negative breast cancer. She is currently being treated with tamoxifen. This case represents a rare presentation of a patient presenting with primary hyperparathyroidism who was ultimately diagnosed with metastatic breast cancer to the parathyroid gland. Rare case reports in the literature have described known breast cancer with spread to the parathyroid gland. This case is unique in that the patient’s breast cancer diagnosis resulted from her primary hyperparathyroidism diagnosis and treatment.