CD9 immunohistochemical staining of breast carcinoma: unlikely to provide useful prognostic information for routine use

Aims: CD9, a cell membrane glycoprotein, is found in a variety of tumour cells and is believed to regulate cell motility and possibly cell growth. It has been reported that the absence of CD9 is associated with increased aggressiveness of breast carcinoma, but no detailed studies of the distribution of CD9 in normal and abnormal breast tissue are available. This investigation was aimed at studying the distribution of CD9 in a wide variety of breast biopsies including normal, benign, and malignant cases, and assessing its usefulness as a prognostic marker in breast cancer. Methods and results: Sections of 113 breast biopsies from female and male patients including 10 normal, 23 benign, and 80 malignant cases were examined. The monoclonal antibody CD9 (Novacastra Ltd, Newcastleupon-Tyne, UK) was used with the avidin-biotin complex immunoperoxidase technique. The results were assessed semiquantitatively using a four scale system of 3+, 2+, 1+ and negative. All normal and benign epithelial cells were strongly stained (3+). In female breast carcinomas, 40% were 3+, 49% were 2+, and 11% were 1+. Both cases of male breast carcinomas scored 3+. For female breast cancers, the results were then correlated to tumour grade, the presence or absence of lymph node metastases, and oestrogen and progesterone receptor status. No significant statistical correlation was found with any of these parameters. We then examined 11 axillary lymph nodes with metastases from some of the above cases. Three of these cases had a CD9 score of 3+, seven were 2+, and one was 1+. The metastatic tumours in all 11 cases were strongly stained (3+). Conclusions: Immunostaining for CD9 is unlikely to provide any useful additional prognostic information for clinical purposes.