The immunohistochemical assay for LCA (Leukocyte Common Antigen) or CD45 aims to detect this tyrosine phosphatase protein found on the surface of all white blood cells (leukocytes), including lymphocytes, monocytes, and neutrophils. It is a highly sensitive and specific marker for hematopoietic cells and is primarily used to confirm or rule out the histological diagnosis of lymphoma by differentiating it from non-hematopoietic tumors (such as carcinoma, sarcoma, and melanoma).