Cluster of differentiation 13 (CD13) is a transmembrane protein present on a number of different tissues and cell types including epithelial and endothelial cells, fibroblasts, leukocytes, and fibroblasts, and is believed to affect tumour progression. It is overexpressed in both haematological and solid malignancies, including Acute Myeloid Leukemia (AML). Although hypogranular variants of AML are difficult to separate from other AML subtypes due to the morphology, through use a panel of CD13(+), CD16(-), CD33(+), CD34(+), and CD117(+), the diagnosis of this variant is possible. Alternatively, a panel of CD13, CD34, CD43, CD68, CD117, CD163, lysozyme, and MPO is very useful for accurately diagnosing myeloid sarcoma and distinguishing it from large cell lymphoma, undifferentiated carcinoma, lymphoblastic lymphoma, malignant melanoma, Burkitt lymphoma, extra-medullary hematopoiesis, and inflammation. Since CD13 is expressed in both normal and neoplastic liver tissues, CD13 staining is useful for distinguishing between hepatocellular carcinoma and non-hepatocellular neoplasms.