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This work was in part supported by the Elsa U. Pardee Cancer Foundation grant (B94AFFAA), the American Cancer Society Research Award (RSG-10-067-01-TBE) and NIH

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**12** 

*Germany* 

**Involvement of Mesenchymal Stem Cells** 

For many reasons, mesenchymal stem cells (MSCs) have lately received much attention. Their plasticity, their tropism for wounds and cancer, their ability to assist in tissue regeneration, their immunomodulary activities, their effects on cancer development and finally their usefulness as drug-delivery vectors made MSCs a prime target for many researchers worldwide. Many aspects of MSC functions have been covered by recent reviews (Beyer Nardi & da Silva Meirelles, 2006; Kidd et al., 2008; Klopp et al., 2011; Krabbe et al., 2005; Patel et al., 2008; Uccelli et al., 2008; Wislet-Gendebien et al., 2005; Yen & Yen, 2008). In this review, we are summarizing the current knowledge on the communication of

Mesenchymal stem cells, also called multipotent mesenchymal stromal cells, were first described as stromal cells residing in the bone marrow (Friedenstein et al., 1966). They have stem cell-like characteristics (Caplan, 1991; Friedenstein & Kuralesova, 1971), a fibroblastlike appearance and features different from cells of the haematopoietic lineages. Those features include the ability to differentiate to osteoblasts, chondrocytes and adipocytes (Friedenstein et al., 1974; Noth et al., 2002; Pittenger et al., 1999). MSCs may also play a role in haematopoiesis, as MSCs have been shown to be involved in forming niches for the haematopoietic stem cells and to regulate the activities of these cells (Ehninger & Trumpp, 2011; Mendez-Ferrer et al., 2010; Omatsu et al., 2010; Sacchetti et al., 2007). MSCs are rare in the bone marrow. Only 1 of 34,000 nucleated cells in this tissue were determined to be MSCs (Wexler et al., 2003). Though much is known about MSCs today, there are still no specific markers available that clearly define a cell as an MSC. In 2006, the International Society for Cellular Therapy published a list of minimal criteria instead (Dominici et al., 2006) that are now commonly used to identify MSCs. Among these criteria are two functional features, the potential to differentiate to osteoblasts, chondrocytes and adipocytes as mentioned above and the ability to adhere to plastic. The latter feature allows the separation of MSCs from the other bone marrow cell populations, as cells of the haematopoietic lineages are nonadherent cells (Beyer Nardi & da Silva Meirelles, 2006). Other critieria used to characterize

MSCs with breast cancer cells and its consequences for breast cancer progression.

**1. Introduction** 

**2. General aspects of MSC biology 2.1 What are mesenchymal stem cells?** 

**in Breast Cancer Progression** 

*Clinic for Gynecology, University of Halle* 

Jürgen Dittmer, Ilka Oerlecke and Benjamin Leyh

pattern of normal and malignant human breast epithelial cells. *Proc Natl Acad Sci U S A* 89, 9064-9068.

