Why is there a need for immunohistochemistry: smooth muscle actin after i got the diagnosis: cellular spindle cell lesion favor nodular fascitis?

To help diagnosis: Pathologists often use immunohistochemistry to help in arriving at a diagnosis. For softn tissue tumors immunohistochemistry can help better characterize the type of tumor...For example if is smooth muscle derived or a neural tumor etc. In terms of nodular fasciitis, it can morphologically appear similar to some smooth muscle tumors and some other fibroblastic tumors so ihc may be used.