Hypercalcemia refers to a condition of calcium levels in blood above the normal range. Most common causes of hypercalcemia include overactivity of parathyroid glands, also known as primary hyperparathyroidism (PHPT), and malignancies. These two disorders contribute to 90% of etiologies leading to hypercalcemia. Various types of cancer manifest hypercalcemia, including breast carcinoma, lung carcinoma, and multiple myeloma. For instance, hypercalcemia is observed in 30% to 40% of patients with breast cancer. The occurrence of hypercalcemia in cancers is attributed to bone metastasis and paraneoplastic syndromes. Malignancies may also be accompanied by PHPT. Therefore, in cancer patients with hypercalcemia, serum parathyroid hormone (PTH) level should be assessed. In the present study, we present a case of breast cancer with hypercalcemia to emphasize the role of PHPT in malignancies.