Mammary carcinoma with osteoclast-like giant cells. Additional observations on six cases.

Six cases of mammary carcinoma with osteoclast-like giant cells are reported. In addition to the multinucleated giant cells and the prominent stromal angiogenesis reported in earlier reports, other characteristic features of the tumors were observed: (1) the gross appearance, characterized by a well-outlined, lump-shaped, dark brown tumor mass; (2) the round tumor shadow on the mammograms, originally interpreted as a cyst, a fibroadenoma, or a medullary carcinoma; and (3) the "adenocystic" pattern of the invasive tumor growth. The light and electron microscopic observations point to the intimate relationship between the tumor cell clusters and the giant cells and provide further support to the theory that these giant cells develop from mononuclear histiocytes in response to the production of some sort of extracellular material by the tumor cells. All of the 26 positive axillary nodes of three patients, and many intramammary lymphatics with tumor thrombi of two patients contained giant cells. These observations indicate that the benign giant cells comprise an integral part of the invasive tumor growth. The six cases were recognized in a series of 527 consecutive breast cancers, during a period of 4 years, in a population of about 75,000 adult women. These data question the reported rarity of this distinctive variant of mammary carcinoma.