Lobular carcinoma of the breast metastatic to bone with unusual clinical, radiologic, and pathologic features mimicking osteopoikilosis.

A 55-year-old woman who underwent a right radical mastectomy for infiltrating lobular carcinoma was found to have multiple diffuse osteoblastic bone lesions. Since she was asymptomatic, had no elevation of alkaline phosphatase, and the lesions did not take up technetium pyrophosphate on bone scan, she was thought to have osteopoikilosis. An iliac bone biopsy was performed that showed greatly thickened bony trabeculae with diffuse delicate marrow fibrosis entrapping easily overlooked short strands of small malignant cells. The histologic picture also closely resembled osteopoikilosis. Although infiltrating lobular carcinoma has been recognized as separate from ductal carcinoma in the primary site, its recognition in metastatic foci is still vague. Attention is drawn to its histologic appearance in skeletal metastases so that such lesions will be more recognizable in the future.