Benign tumors of the breast with multinucleated stromal giant cells. Immunohistochemical analysis of six cases and review of the literature.

The authors present six cases of benign tumors of the breast with numerous multinucleated stromal giant cells (MSGC). All six patients were women aged 37-70 years (mean 48 years), presenting clinically with a breast mass 1.0-3.8 cm in size (mean 1.9 cm; median 1.5 cm). By standard H&E examination, all cases showed the presence of numerous MSGC haphazardly dispersed within the tumor stroma. Three cases revealed MSGC merging into the surrounding adipose tissue simulating infiltrative growth. The MSGC appeared to have multiple nuclei (5 to 25) with fine chromatin and sporadic small nucleoli. Their cytoplasm was inconspicuous. The MSGC expressed vimentin only and to lesser extent CD34. These cells were negative for muscle markers, keratins, S-100 protein, vascular markers, CD68 and hormone receptors. Interestingly, the majority of MSGC and mononuclear stromal cells showed reactivity for p53 protein and Ki-67 proliferation antigen. All patients were treated by simple excision and remain free of recurrence (mean 70 months, median 48 months.). The reactivity of p53 in MSGC and mononuclear stromal cells may play a key role in linking these two cell types. Nonetheless, the presence of MSGC does not alter prognosis of otherwise typical benign lesions.