Intense uptake of technetium-99m-MDP in primary breast adenocarcinoma with sarcomatoid metaplasia.

Focal soft-tissue accumulation of bone-seeking radiopharmaceuticals has many causes but is usually less intense than skeletal activity. Extraskeletal new bone formation, as seen in myositis ossificans and extraskeletal osteosarcoma, represents an exception where markedly increased uptake can be seen. Technetium-99m-MDP uptake in primary breast carcinoma has been recently investigated using scintamammographic techniques to differentiate malignant from benign lesions. The mechanism of uptake remains unclear but is likely multifactorial and nonspecific. We present a case of primary breast carcinoma with florid 99mTc-MDP activity relative to normal bone. Tumor histopathology in this patient demonstrates malignant new bone formation as the likely mechanism for the marked radiotracer avidity.