In the small sets of human samples we studied for total pRb expression by western and phospho-pRb expression by immunohistochemistry, we found that overall expression was generally low for aRMS tumors (similar to the mouse), and that only subsets of cells had expression within a tumor mass (and among this subset, cytoplasmic localization for presumed pRb inactivation was not uncommon). Here, RB1 is linked to neoplasm.