Metastatic breast cancer from an occult primary provisionally identified by steroid receptor content and two-dimensional protein electrophoresis: some problems associated with the use of the latter technique.

Occult primary breast cancer in a patient presenting with undifferentiated metastatic adenocarcinoma in an inguinal lymph node was provisionally diagnosed by the steroid receptor content of its metastases and by the sclerotic pattern of osseous metastases. This diagnosis was supported by the presence of several proteins electrophoresed in 2 dimensions that may be common to other identified adenocarcinomas of the breast. These proteins appear to be absent from a representative adenocarcinoma of the ovary and of the uterus, at least at the level of sensitivity provided by the dye used to detect them. Some clinical implications for the use of two-dimensional protein electrophoresis in identifying undifferentiated cancers are considered.