CD34⁺ fibrocytes can be found in the stroma of virtually all human organs (pancreas, cervix, breast ). In most cases of invasive carcinoma (see below) the tumor associated stroma is devoid of CD34⁺ fibrocytes and SMA reactive myofibroblasts -which generally are not found in normal connective tissue- can be observed. Detection of a loss of CD34⁺ fibrocytes paralleled by a gain of SMA reactive myofibroblasts may also be helpful in distinguishing radial scars and tubular carcinomas of the breast. CD34⁺ fibrocytes are capable of matrix-synthesis (Collagen I) and antigen-presentation (for review see CN Metz), the significance of a loss of CD34⁺ fibrocytes for tumor invasion and distant spread remains to be elucidated.

     

The interface between tumor free stroma (left) and invasive carcinoma of the breast is characterized by an abrupt loss of CD34⁺ fibrocytes. CD34 decorates endothelial cells of vessels located within the tumor stroma (CD34). Right: the loss of CD34⁺ fibrocytes is in most cases accompanied by a gain of SMA reactive myofibroblasts (adenocarcinoma of the pancreas, SMA, Barth et al., 2002).

Stromal myofibroblasts found in squamous cell carcinomas of the upper aero-digestive tract were observed to express CD117 in about 60% of cases investigated (squamous cell carcinoma of the larynx, CD117, Barth et al, 2004). 

CD34⁺ fibrocytes also occur in the stroma of the mitral valve and it appears that they are significantly involved in the pathogenesis of  myxoid mitral valve disease.

In carcinomas of the breast stromal remodelling is closely related to increased expression of SPARC (secreted protein rich in cysteine); the respective paper has recently been published in Virchows Archiv. 

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References 

See also:

FIBROCYTES
New Insights into Tissue Repair and Systemic Fibroses

edited by Richard Bucala (Yale University, USA)

CD34+ Fibrocytes: Morphology, Histogenesis and Function