Paraneoplastic syndromes are caused by ectopic hormone production in malignant tumors. Hypercalcemia of malignancy is
the main manifestation of paraneoplastic syndromes and can lead to acute kidney injury, life-threatening arrhythmia, and cardiac
arrest. Here, we present a 70-year-old Asian female with a probable diagnosis of advanced lung cancer with hypercalcemia of
malignancy. She underwent surgery to treat a pathologic fracture of the humerus. In this case, hypercalcemia of malignancy was
unexpectedly aggravated after surgery, and hypercalcemic complications led to a poor outcome for the patient.