Introduction The incidence and mortality of endometrial cancer (EC) is rising worldwide. The biological underpinnings of EC progression are poorly understood. We sought to characterize the genetic alterations and clonal evolution of two primary high-grade ECs and their matched multiple distant metastases.

Methods Research autopsies were performed on two women: one with treatment-naïve, widely metastatic undifferentiated carcinoma at diagnosis (case 1); and one with serous EC and heavily treated metachronous disease (case 2). Whole-exome sequencing of primary tumors, metastases (n=8 and n=7), and normal tissues was performed and analyzed using validated bioinformatics methods.

Results In case 1, truncal hotspot PIK3CA p.Q546K and PTEN p.R130G mutations, chromosome 8 and 16p losses, and mutational aging signature 1 were present in the primary and all metastases. Low levels of genetic heterogeneity between all samples were observed (70% of mutations shared). In case 2, we found high levels of genetic heterogeneity and acquisition of mutations during progression. A truncal PIK3CA p.H1047L hotspot mutation was present in the primary tumor and all metastases, with a primary subclonal TP53 frameshift mutation becoming clonal in a subset of metastases (n=3). Evidence of clonal progression between metastatic sites was observed as well as a combination of aging and homologous recombination-deficiency mutational signatures.

Conclusion Genetic alterations identified in case 1 were likely early events in the clonal expansion of the primary tumor, reflective of aggressive disease and absence of treatment. In case 2, evidence of clonal diversity and progression was observed, potentially representing clonal selection due to therapeutic effect.