CD44 and prostate cancer: A recent study by Kroon and coworkers provided evidence that most primitive populations of prostate cancer cells (i.e., CD44+CD133+) express 6-fold to 7-fold higher IL-6 levels than the more mature tumor cells (i.e., CD44+CD133-) and IL-6 receptor is expressed on progenitor cancer cells and is activated by IL-6, with consequent STAT3 activation.