Expression of steroid hormone receptors, their regulated proteins, and bcl-2 protein in myofibroblastoma of the breast

Aims: To investigate the possible role of steroid hormones in the pathogene sis of myofibroblastoma (MFB) of the breast, we analysed the immunohistoche mical expression of oestrogen, progesterone, androgen receptors, their regu lated proteins and bcl-2 protein in a series of this rare tumour. Methods and results: Paraffin-embedded sections from seven cases of MFB of the breast (five male; two female) were immunohistochemically tested for th e expression of oestrogen receptor (ER), progesterone receptor (PR), androg en receptor (AR), oestrogen-regulated pS2 protein, androgen-regulated prost ate-specific antigen (PSA) and bcl-2 protein. Rare cases of benign spindle cell tumours or tumour-like lesions of the breast (primitive fibromatosis, inflammatory pseudotumour, muscular hamartoma) which enter into the differe ntial diagnosis with MFB, were also investigated and compared with MFB. All cases of MFB showed a diffuse (70-90% of neoplastic cells) and strong nucl ear labelling with ER and PR, whereas AR was expressed only in three cases (two men and one woman) in about 60-70% of cells. Conversely, no immunostai ning was detected for the pS2 protein and PSA. bcl-2 protein immunoreactivi ty was found in all cases of MFB, although with a variable degree of expres sion. No expression for steroid hormone receptors, their regulated-proteins and bcl-2 protein was observed in the rare benign spindle cell lesions of the breast included in this study. Conclusion: The in-situ detection of ER, PR and AR suggests that steroid ho rmones and their receptors are implicated in the pathogenesis of breast MFB . The consistent demonstration of bcl-2 protein, associated with a positive ER/PR status, provides evidence that bcl-2 may be an oestrogen-regulated p rotein also in MFB and that probably plays a role in the tumorigenesis. Fin ally, we postulate that the ER/PR and bcl-2 positive immunoprofile of MFB o f the breast, in contrast to the negative profile of other rare primitive b enign spindle cell lesions of the breast herein studied, might be exploited as an ancillary diagnostic aid in differential diagnosis of doubtful cases .