Purpose and experimental design: Lymphovascular space invasion plays a critical role in the progression of cervical cancer and is an indicator of an unfavorable prognosis, even in patients with early-stage disease. Identification and functional characterization of molecules that are predominantly expressed in tumors able to penetrate lymphatic vessels may therefore help to improve the clinical assessment of cervical neoplasias with unclear prognosis. We used immunohistochemical staining to assess expression of the tetraspanin adapter protein CD9 in cervical tumors because inverse correlations with tumor invasiveness, ability to form metastases, and poor clinical outcome have been described for several other tumor types.
Results and conclusion: We found that CD9, strongly expressed by cells forming the basal layer of normal squamous epithelium of the cervix, is down-regulated in most invasive cervical carcinomas (correlation with stage, P = 0.015) but apparently re-expressed at distinct regions during tumor progression. Tumor sites with pronounced localized expression of CD9 (CD9 hotspots) include cones growing into blood or lymphatic vessels, pointing to a functional role of CD9 in transendothelial migration as a crucial step in the formation of lymph node metastases. Remarkably, CD9 hotspots were found to be a highly significant (P < 10(-5)) indicator of lymphangiosis: they were observed in 15 of 18 cases with histopathologically confirmed lymphangiosis compared with 4 of 26 other cervical carcinomas. We postulate, therefore, that clusters of tumor cells characterized by strong expression of CD9 may be useful as an indicator of high risk of recurrence in early-stage cervical cancer, providing a basis for clinical decisions in favor of additional treatment.