A 50-year-old woman presents with lower back pain of 3 weeks in duration. Radiologic studies reveal several discrete lytic lesions in the lumbar back and pelvis. Laboratory studies show elevated serum levels of alkaline phosphatase. Serum calcium, serum protein, and peripheral blood smears are normal. Aspiration biopsy of a pelvic lesion shows keratin-positive cells. Which of the following is the most likely diagnosis?

Multiple lytic lesions associated with keratin-positive cells strongly suggest metastatic bone cancer. Metastatic carcinoma is the most common tumor of bone, and skeletal metastases are found in at least 85% of cancer cases that have run their full clinical course. The vertebral column is the most commonly affected bony structure. Tumor cells usually arrive in the bone by way of the bloodstream. Some tumors (thyroid, gastrointestinal tract, kidney, neuroblastoma) produce mostly lytic lesions. A few neoplasms (prostate, breast, lung, stomach) stimulate osteoblastic components to make bone. The other choices are not keratin positive.Diagnosis: Metastatic bone cancer