Therefore, the diagnosis of UPS is commonly based on detecting a specific set of proteins that are expressed by UPS tumor cells but not by the cells of other undifferentiated and pleomorphic tumors or visa versa (see Diagnosis section).A study of 52 individuals found that their UPS tumor cells expressed on their surface membranes PD-L1 protein (i.e. programmed death-ligand 1 protein) either focally (36.5% of cases) or strongly (9.62% of cases); 48.1% of these individuals had tumor cells which also expressed IDO1 protein (i.e. indoleamine 2,3-dioxygenase protein). Tumor cells that strongly expressed PD-L1 also expressed CMTM6 protein (i.e. CKLF like MARVEL transmembrane domain containing 6 protein). Strong PD‑L1 expression proved to be a poor, while expression of IDO‑1 proved to be a favorable, prognostic factor for disease outcomes. Individuals with tumor cells that strongly expressed CMTM6 protein also had poor prognoses. Increases in the expression of CMTM6 protein were associated in some cases with mutations that increased the number of copies of its gene, i.e. CMTM6. In a later study that examined 83 individuals, 72.8% had UPS tumor cells that expressed PD-L1 with 53%, 35%, and 12% of these cases showing weak, intermediate, and strong PD-L1 expression, respectively. And, in a study of 73 patients with UPS, 39 cases showed no, 23 cases showed low, 10 showed intermediate, and 11 strong  immunoreactivity for AMPD2, i.e.
is responsible for production of) the retinoblastoma protein that functions as a tumor suppressor protein; 2) deletions and/or mutations in the TP53 gene that encodes tumor protein P53 (a protein which regulates cell proliferation and cell death); 3) mutations in the ATRX gene that encodes transcriptional regulator ATRX protein which contributes to regulating the expression of various genes; 4) mutations in the KMT2C gene which encodes lysine N-methyltransferase 2C protein (the KMT2C gene is mutated in various cancer types); 5) amplification of the IL7R gene which encodes Interleukin-7 receptor-α protein (mutations in the IL7R gene are commonly found in acute lymphoblastic leukemia) and 6) expression of a fusion gene (i.e. a hybrid gene formed from two previously independent genes as a result of a mutation) that merges TRIO with other genes and is often found in other sarcoma subtypes.) Diagnosis
The diagnosis of UPS depends on finding non-specific, undifferentiated tumor cells that have features suggestive of UPS and not features of other tumor types that also consist of pleomorphic, undifferentiated cells. The features primarily involve the expression of certain proteins by the tumor cells. The identifying proteins for UPS tumor cells are given in the preceding section. Identification proteins for tumors that have been confused with UPS inlclude:
Pleomorphic leimyosarcoma: Desmin and h-caldesmon (i.e. high molecular form of caldesmon.) proteins
Pleomorphic rhabdomyosarcoma: Desmin and myogenin proteins. Defifferentiated liposarcoma: MDM2 and CDK4 proteins. Poorly differentiated carcinoma (i.e.