We classify endometrial cancer so that we can communicate and define each patient’s disease status, the potential for harm, and the likelihood that adjuvant therapies might provide help. Traditional forms of classification have clearly fallen short in achieving this aim, as we all know of patients with apparent low-risk disease (such as stage IA grade 1 endometrioid carcinoma) who have had recurrences and died from their disease, and we know that many patients have been subjected to overtreatment for their cancer and have acquired lifelong toxicities of therapy. This column will explore the newer, more sophisticated molecular-based classifications that are being validated for endometrial cancer, and the ways in which this promises to personalize the treatment of endometrial cancer.
Breast cancer and melanoma are examples of the inclusion of molecular data such as hormone receptor status, HER2/neu status, or BRAF positivity resulting in advancements in personalizing therapeutics. We are now moving toward this for endometrial cancer.
What is the Cancer Genome Atlas?
In 2006 the National Institutes of Health announced an initiative to coordinate work between the National Cancer Institute and the National Human Genome Research Institute taking information about the human genome and analyzing it for key genomic alterations found in 33 common cancers. These data were combined with clinical information (such as survival) to classify the behaviors of those cancers with respect to their individual genomic alternations, in order to look for patterns in mutations and behaviors. The goal of this analysis was to shift the paradigm of cancer classification from being centered around primary organ site toward tumors’ shared genomic patterns.
In 2013 the Cancer Genome Atlas published their results of complete gene sequencing in endometrial cancer.3 The authors identified four discrete subgroups of endometrial cancer with distinct molecular mutational profiles and distinct clinical outcomes: polymerase epsilon (POLE, pronounced “pole-ee”) ultramutated, microsatellite instability (MSI) high, copy number high, and copy number low.
An important subgroup identified in the Cancer Genome Atlas was a group of patients with a POLE ultramutated state. POLE encodes for a subunit of DNA polymerase, the enzyme responsible for replicating the leading DNA strand. Nonfunctioning POLE results in proofreading errors and a subsequent ultramutated cellular state with a predominance of single nucleotide variants. POLE proofreading domain mutations in endometrial cancer and colon cancer are associated with excellent prognosis, likely secondary to the immune response that is elicited by this ultramutated state from creation of “antigenic neoepitopes” that stimulate T-cell response. Effectively, the very mutated cell is seen as “more foreign” to the body’s immune system.
Approximately 10% of patients with endometrial cancer have a POLE ultramutated state, and, as stated above, prognosis is excellent, even if coexisting with a histologic cell type (such as serous) that is normally associated with adverse outcomes. These women tend to be younger, with a lower body mass index, higher-grade endometrioid cell type, the presence of lymphovascular space invasion, and low stage.
MSI (microsatellite instability) is a result of epigenetic/hypermethylations or loss of expression in mismatch repair genes (such as MLH1, MSH2, MSH6, PMS2). These genes code for proteins critical in the repair of mismatches in short repeated sequences of DNA. Loss of their function results in an accumulation of errors in these sequences: MSI. It is a feature of the Lynch syndrome inherited state, but is also found sporadically in endometrial tumors. These tumors accumulate a number of mutations during cell replication that, as in POLE hypermutated tumors, are associated with eliciting an immune response.