The diagnosis of low-grade and pseudosarcomatous spindle cell lesions of skin and soft tissue can sometimes be problematic; in particular, distinction between fibroblastic, myofibroblastic, and smooth muscle proliferations can occasionally pose difficulties on routine histologic examination. We have applied a panel of immunohistochemical markers to a series of spindle cell lesions of skin and soft tissue to assess the utility of the differential expression of smooth muscle and myofibroblastic-associated markers. Twenty-eight cases of nodular
fasciitis, 42 cases of
fibromatosis, and 3 cases of myofibroblastic
sarcoma were stained with
antibodies against smooth muscle actin (SMA), smooth muscle
myosin (SMMS),
calponin, and high-molecular weight
caldesmon (h-
caldesmon). For comparison, 12 cases of cutaneous
leiomyoma and 8 cases of
leiomyosarcomas involving superficial soft tissues and fascia were studied with the same panel of
antibodies. Thirty-eight of 42 cases of
fibromatosis were positive for SMA, 42/42 cases were positive for
calponin, 39/42 cases were negative for SMMS, and all cases were negative for h-
caldesmon. All cases of nodular
fasciitis were positive for SMA and
calponin, and all were negative for h-
caldesmon and SMMS. All cases of myofibroblastic
sarcoma were positive for SMA and 2/3 cases for
calponin, and were negative for SMMS and h-
caldesmon. All cases of cutaneous
leiomyoma and
leiomyosarcoma were positive for all 4 markers tested. Our results demonstrate a remarkably consistent pattern of reactivity of muscle and myofibroblastic-associated markers in lesions predominantly composed of myofibroblastic spindle cells, characterized by positive staining for SMA and
calponin and absence of reactivity for SMMS and h-
caldesmon. Application of this panel of stains may be of aid in the differential diagnosis of low-grade myofibroblastic lesions such as nodular
fasciitis and
fibromatosis from
smooth muscle tumors of skin and soft tissue. This panel may additionally be of assistance in the diagnosis of myofibroblastic
sarcoma.