Invasive breast carcinomas of no special type with osteoclast-like giant cells frequently have a luminal phenotype.

Invasive carcinoma of no special type (NST) with osteoclast-like giant cells (OGCs) represents a unique type of breast neoplasm, characterized by the presence of multinucleated OGCs and a vascularized, hemorrhagic stroma. Because of its rarity, the literature regarding this tumor remains limited and a detailed immunophenotype of this tumor has not been established as yet. We report a clinicopathological and immunohistochemical study of 42 patients with invasive carcinoma NST with OGCs. Macroscopically, these tumors presented as a well-delimited red-brown mass. A remarkable feature of the tumor was the presence of OGCs in the fibroblastic or hemorrhagic vascular stroma, as well as in the adjacent tumor nests or glandular lumina. The number of OGCs varied from 8 to 105 per 10 high-power fields with an average of 48. The tumors were well to moderately differentiated. Cribriform architecture was observed in 27 tumors (63 %). All of the 36 available tumors were of luminal phenotype, according to the Ki67 labeling index 89 % luminal A and 11 % luminal B. With a mean follow-up time of 46.4 months, lung metastasis was found in 2 patients (5 %) at 7 and 11 years after the operation, respectively. None of the other cases had presented with evidence of recurrence or metastasis. To the best of our knowledge, this is the largest reported series of invasive carcinoma NST with OGCs as yet. Our study revealed that invasive carcinoma NST with OGCs exhibit a luminal phenotype with luminal A subtype as the major group.