Hereditary, molecular and prognostic factors in endometrial cancer

Abstract

Aims: The overall aim of this thesis is to describe and evaluate hereditary uterine cancer syndrome both independent of and in relation to hereditary patterns of Lynch and/or Cowden syndrome for the purpose of recognizing and defining a unique pattern of familial uterine cancer. The thesis also aims to determine whether the TERT-CLPTM1L region is a novel risk locus for endometrial cancer. Finally, we aim to assess expression of two mitochondrial proteins, PGC1α and VDAC1, within the same population, as well as to consider the impact of different dietary and lifestyle factors on prognosis for endometrial cancer (EC).

Materials and methods: All studies are retrospective and based on a cohort population of women who were diagnosed with endometrial cancer and underwent surgery at Karolinska Hospital, Stockholm, Sweden, between January 1, 2008 and March 31, 2012. All women who agreed to participate completed questionnaires, one concerning family history of cancer and the other regarding personal health history including comorbidity, parity, medications, lifestyle and dietary habits. Data on clinicopathological variables were obtained from the Take Care medical records system.

In study I we constructed pedigrees based on the questionnaires with verification by telephone interview, assessed the relative frequencies of various cancers among family members and compared those with the general Swedish population in 1970 and 2010. Study II entails a collaborative effort, known as the Endometrial Cancer Association Consortium (ECAC), in which 5591 women of European ancestry with a history of histologically verified diagnosis of endometrial cancer were enrolled into 11 separate studies conducted in Western Europe, North America, and Australia. The Swedish contribution to this multi-center study derives from the Registry of Endometrial Cancer in Sweden (RENDOCAS), which is a hospital-based registry of consecutively occurring EC cases. The study included 262 cases of EC taken from the same group as Study I and enrollment continued until 2011. In addition to the above information, DNA samples for each patient were obtained from peripheral blood. In Study III, both tumor and adjacent benign tissue were analyzed using immunohistochemistry and subsequently scored to assess PGC1α and VDAC1 expression in both types of tissue and to correlate these findings with clinical data. In Study IV a smart machine learning model, Random Survival Forest, was used to analyze the extensive data and correlate them with prognosis for endometrial cancer.

Results: In Study I we found an increased prevalence of EC among our study population compared with the general population in Sweden in 1970 and 2010. Lynch syndrome, as defined according to the Amsterdam II criteria, was found in 7 families. In all, 13% of index patients had at least one relative with EC and these families showed a tendency for more cases of early onset cancer among family members. In study II, data concerning single nucleotide polymorphisms (SNPs) taken from the 5p15 region were available from 4401 cases and 28 758 controls. Using logistic regression, we found three imputed SNPs (rs7705526 (in SNP set 1), rs13174814 (SNP set 2) and rs62329728 (SNP set 3)) that each showed evidence of being independently associated with disease for which the respective ORs were 1.11, 0.87 and 1.27 by unconditional analysis. The linkage disequilibrium (LD) between these three SNPs is weak, which further suggests that they represent independent risk factors for endometrial cancer. When comparing with data taken from the cancer genome atlas (TCGA), we were able to identify higher expression of TERT-CLPTM1L RNA in EC tissue than found in normal tissue. Study III found that both PGC1α and VDAC1 showed significantly lower expression in tumor tissue compared with benign tissue. We also observed a correlation trend indicating an association between low PGC1α expression and shorter time to death among patients in the FIGO I group. The study IV analysis revealed that consumption of fried potatoes and carbonated soft drinks is higher among women with recurrent endometrial cancer and death.

Conclusions: Our study found an overrepresentation of EC among first- and second-degree relatives, as well as first cousins of endometrial cancer patients, when compared with the general population. Young age of onset and occurrence of multiple cancers in families with EC suggest the presence of additional factors relating to hereditary EC syndrome. We emphasize the importance of accurate diagnosis, with referral for genetic counseling, and improved surveillance of individuals at high risk for EC. In study II we succeeded in uncovering a novel risk locus for EC and implicated three novel independent genetic variants within the 5p15 locus (already associated with several cancers) that increase risk of developing EC. Overexpression of TERT in cases of EC when compared with normal tissue suggests a potentially important role for this gene in tumorigenesis. Our findings may account for about 0.5% of the relative risk for familial EC. Study III found downregulation of both PGC1α and VDAC1 in malignant tissue, as well as a correlation between low PGC1α expression and shorter time to death among patients in the FIGO I group. This correlation has important clinical implications since these patients are treated exclusively by surgery. Should lower expression of PGC1α correlate with increased risk of recurrence, new therapeutic strategies may be required. In study IV we observed that consumption of fried potatoes and sweetened carbonated beverages is associated with higher risk of recurrence and death from EC. Dietary modification may therefore be advisable for women with endometrial cancer.