Proteomic characterization of intra-tumor heterogeneity in human endometrial cancer.

Endometrial cancer (EC) is one of the most frequently diagnosed gynecological cancers worldwide, and its prevalence has increased by more than 50% over the last two decades. Despite the understanding of the major signaling pathways driving the growth and metastasis of EC cells, clinical trials targeting these signaling pathways in human patients have reported poor outcomes. Heterogeneous nature of EC is suspected to be one of the key reasons for the failure of targeted therapies. However, no study so far has explored EC heterogeneity within the same patient at the proteomic level. In this study, we isolated proteins from tumor tissue samples obtained from different sites of EC from individual patients (~2-4 samples/patient). We then performed a SWATH-based comparative proteomic analysis, using liquid chromatography-tandem mass spectrometry (LC-MS/MS), to profile the protein content of different areas within EC tissue. Our results highlighted an average of 1424 unique proteins in 20 patient-derived EC tissues with a confidence corresponding to a false discovery rate below 1%. We have identified protein biomarkers that differentiate between premenopausal vs postmenopausal cancer, macroscopic vs microscopic tumor, more vs less invasive cancer, and DNA mismatch repair defective vs intact tumor. Furthermore, the data revealed a list of unique proteins that, for the same patient, exist only in a single EC location but are not present in other locations within the same tumor. Overall, our proteomic analysis highlighted that tumor tissue samples collected from different sites of EC within the same patient can harbor diverse protein profiles. Importantly, this study sets the foundation for further investigations into the mechanisms of endometrial heterogeneity and some of the proteins identified here may represent potential novel EC drug targets