Oncologic Trogocytosis Figure 8. Clinical relevance of the presence of Hospicells among ovarian cancer tumors. Tissue Micro-arrays were prepared from tumors originating from 29 patients who underwent a neo-adjuvant chemotherapy. A. Different densities of Hospicells as represented by CD10 staining. Morphological controls were used to rule out the staining of endothelial cells. B. Samples from chemoresistant patients had significantly higher density of Hospicells compared to chemosensitive patients (* p,0.05). Three different spots were used to characterize the Hospicells’ density for each patient. doi:10.1371/journal.pone.0003894.g008 metastatic niche was constituted from CD34-positive progenitors, however the exact composition of the niche is not illustrated in their study. We can hypothesize that the pre-metastatic niche is a complex microenvironment such as the stem cell niche. Different cellular subtypes might then have different roles in promoting metastasis. Our cell type may act as a ‘‘feeder’’ cell in the initiation of the metastatic process. Moreover stem cells from a variety of tissues express high levels of ABC transporting proteins that play a role in cytoprotection through the excretion of genotoxic and xenobiotic compounds out of the cells [35]. These latter properties might therefore create a ‘‘drug-free’’ niche that will be more suitable to cancer cells development. Hospicells also displayed positivity for other markers. CD9 is a member of the tetraspanin family. These proteins mediate signal transduction events and play a role in the regulation of cell development, activation, growth and motility and intercellular interactions. CD9 in particular plays a role in fusion between the spermatozoide and the ovocyte. In addition, it promotes muscle cell fusion and support myotube maintenance [36–38]. CD9 down regulation on ovarian cancer cells seem to be associated to higher histological grade and metastatic progression. The role of CD9 expression on stromal cells in ovarian cancer has not been established [39]. CD10 is a neutral endopeptidase (NEP) also known as common acute lymphoblastic leukemia antigen (CALLA). It is a zinc-dependent metalloprotease enzyme that degrades a number of small-secreted peptides. Associations have been observed between CD10 overexpression on cancer or stromal cells and various types of cancer such as ovarian cancer or advanced melanoma [40,41]. CD10 was specifically expressed in the stroma of borderline and malignant ovarian tumors, but not in adenomas. Furthermore, stromal CD10 was downregulated as the histological grade advanced. These results suggest that CD10 may play a role in the regulation of neoplastic transformation and tumor differentiation in epithelial ovarian carcinomas. Similarly the presences of CD10 positive cells have not been assessed in ovarian cancer so far. CD166 or ALCAM. Decreased/lost ALCAM membrane expression is a marker of poorer outcome in epithelial ovarian cancer. CD166 has recently been described as a marker of the bone marrow stromal cells capable of supporting hematopoiesis [42,43]. Its specific role in ovarian cancer has not PLoS ONE | www.plosone.org 9 December 2008 | Volume 3 | Issue 12 | e3894