Enchondroma on bone scan in a patient with breast cancer.

A 45-year-old postmenopausal woman with breast cancer was treated with modified radical mastectomy and radiotherapy. She remained clinically well for two years but then complained of pain in the left upper arm during a routine follow-up visit with her physician. A roentgenogram of the left proximal humerus showed a densely sclerotic, nonhomogeneous, 2 x 6 cm lesion with stippled calcification, the appearance of which was most consistent with a mature enchondroma or bone infarct. Because metastatic breast cancer was also a possibility, a technetium Tc 99m methyldiphosphonate (MDP) bone scan was done, revealing diffuse uptake in the left proximal humeral lesion, without any other area of involvement. Although radiologically the lesion appeared benign and stable, the history of breast cancer, abnormal bone scan, and pain could not be ignored, and open surgical bone biopsy was done. From deep within the lesion at the core of the metaphysis of the proximal left humerus, the surgeon removed an enchondroma, but found no evidence of metastatic disease. Follow-up MDP bone scans after six months and four years were unchanged.