Specific but variable expression of h-caldesmon in leiomyosarcomas - An immunohistochemical reassessment of a novel myogenic marker

h-Caldesmon is considered a novel specific marker for tumors with smooth mu scle differentiation. To reassess its diagnostic use, the authors evaluated the immunohistochemical expression of h-caldesmon and other myogenic marke rs (calponin, a-smooth muscle actin, HHF35, and desmin) in 30 leiomyosarcom as (external soft tissues [15], retroperitoneum [8], uterus [5], other site s [2]), 26 myofibroblastic lesions, and 26 fibrohistiocytic tumors of varyi ng biologic potential and histology. In contrast with previous data, h-cald esmon was expressed only in 11 (36%) of the 30 leiomyosarcomas analyzed, wh ereas they consistently expressed actins and frequently expressed calponin (86%) and desmin (76%). Leiomyosarcomas with the expression of h-caldesmon were well or moderately differentiated and primarily confined to the retrop eritoneum or uterus. All but one leiomyosarcomas in the external soft tissu es examined were negative for h-caldesmon, and the h-caldesmon-negative tum ors showed moderately to poorly differentiated morphology. All myofibroblas tic lesions examined were negative for h-caldesmon despite their constant e xpressions of at least one of the other markers. h-Caldesmon was not expres sed in fibrohistiocytic tumors either, although focal positivity for the ot her markers was seen in subsets of the tumors. Thus, h-caldesmon can be reg arded as a specific myogenic marker. However, one should be aware that the expression of h-caldesmon in leiomyosarcomas can be more variable according to their locations and/or extent of smooth muscle differentiation than con sidered previously.