There is no data that supports the hypothesis that Rebif (interferon-beta) causes feminization of a male body. Feminization is not typical for multiple sclerosis, either. You can consult an endocrinologist first in order to investigate the symptoms of growing breasts and feminine behavior. A hormonal analyses (testosterone, estrogen, FSH, LH, prolactin) can be requested to begin the diagnostic process of identifying the cause for these symptoms.