Endometrial adenocarcinoma is the most frequently diagnosed type of gynecological malignancy, with 280,000 cases reported worldwide in 2008 (1). In the United States, it is estimated that there were ~40,000 new cases per year, with 7,500 mortalities reported in 2008 (2). The majority of cases are grade 1 endometrioid-type adenocarcinoma confined to the uterus for which total hysterectomy and bilateral salpingo-oophorectomy is standard treatment (1,2). However, a small but significant percentage of cases recur following total hysterectomy. This recurrence, or cases that are metastatic upon presentation, exhibit a limited response to systemic therapy (chemotherapy, hormonal therapy or radiation). The five-year survival rate is >95% for women with disease confined to the uterus (stage I) and ~15% for distant, high-stage disease (3). Recently, The Cancer Genome Atlas (TCGA) project stratified endometrioid endometrial adenocarcinoma (EEC) into four different molecular subgroups, each with distinct survival outcomes: i) Copy-number low (CNL) alterations; ii) copy-number high alterations (serous-like); iii) polymerase ε (POLE) ultramutated; and iv) microsatellite instability hypermutated (4). In this stratification system, the CNL-EEC molecular subgroup exhibited intermediate progression-free survival compared with the POLE ultramutated (best prognosis) and copy-number high, serous-like (worst prognosis) tumors (4).

Similar to previous studies, which revealed a high percentage of somatic phosphatase and tensin homolog (PTEN), phosphoinositide-3-kinase catalytic subunit alpha (PIK3CA) and PI3K regulatory subunit 1 (PIK3R1) mutations in EECs, the TCGA study revealed that a significant number of endometrial adenocarcinomas had genetic alterations in the PI3K/AKT pathway, suggesting a potential for targeted therapy with specific inhibitors (4–11). More specifically, TCGA demonstrated that the PI3K pathway was altered in 92% (83/90) CNL-EEC cases, as evidenced by somatic mutations in the PTEN, PIK3CA and PIK3R1 genes (4). The majority of CNL-EEC tumors (77%; 69/90) exhibited somatic PTEN mutations, while approximately half (53%; 48/90) exhibited somatic PIK3CA mutations and one-third (33%; 30/90) contained somatic PIK3R1 mutations. Furthermore, approximately two-thirds of tumors (68%; 61/90) exhibited somatic mutations in >1 member of the PI3K pathway (4). These and previous findings (4–11) support the hypothesis that activation of the PI3K signaling pathway is an important step in the development of EEC.

The aim of the present study was to investigate whether mutations of PI3K pathway members are associated with specific survival outcomes in patients with endometrial adenocarcinomas and whether these outcomes are specific to a particular molecular subgroup.

Clinical data from 307 newly diagnosed endometrial carcinoma patients with endometrioid-type histology, including 90 cases of the CNL-EEC subtype, was obtained from TCGA Research Network (4) and integrated with PIK3CA mutation data from TCGA Data Portal via the cBio Cancer Genomics Portal (4,17,18). Survival analysis of all TCGA tumors with endometrioid-type histology (n=307), regardless of molecular subtype, revealed that patients with somatic PIK3CA mutations exhibited significantly improved overall survival and marginally prolonged progression-free survival compared with those possessing wild-type PIK3CA (log-rank test P=0.001 and P=0.077, respectively; Fig. 1A and B).

The overall survival outcome difference was specific to the CNL-EEC patients (n=90; P=0.018; Fig. 1C and D), as no significant association with overall and disease-free survival was observed in the three other TCGA molecular subgroups (copy-number high, P=0.442 and P=0.225; POLE ultramutated, no mortality or recurrence; or microsatellite instability hypermutated tumors, P=0.108 and P=0.949) (data not shown). For this reason, the remainder of the study was focused on the CNL-EEC subgroup. In CNL-EEC, the mean follow-up times for patients with mutated and wild-type PIK3CA were 33 and 26 months, respectively. The median follow-up times for patients with mutated PIK3CA and wild-type PIK3CA were 29 and 21 months, respectively. There were no reported mortalities among patients with PIK3CA mutations (0%; 0/48), while 4 mortalities were reported among the patients with wild-type PIK3CA (9.5%; 4/42). Of the patients with somatic PIK3CA mutations, 5 exhibited recurrent disease (10.4%; 5/48), while 8 patients with wild-type PIK3CA had recurrent disease (19.0%; 8/42).

Next, the pathological data was re-reviewed in terms of patient age, tumor type, stage and FIGO grade via the tools available at TCGA Data Portal Open-Access directory and the cBio portal. Patient age in PIK3CA-mutated cases ranged from 34–89 years (mean, 60.3 years; median, 60 years), which was similar to that of the non-mutated cases (range, 37–90 years; mean, 60.6 years; median, 59 years) (Table I). The majority of PIK3CA-mutated cases were of stage I (83%; 40/48) and FIGO grade 1 or 2 disease (48 and 44%, respectively) (Table I and Fig. 2). There were no significant differences in age, tumor stage and FIGO grade between PIK3CA-mutated and non-mutated cancers (Table I). For all cases in the CNL-EEC subgroup, the tumors were of endometrioid histological type. This was confirmed by the presence of back to back atypical endometrial type glands with complex architecture, no intervening stroma and varying differentiation upon review of available H&E images (Fig. 2).

Pathological analysis of 3 PIK3CA-mutated cases also demonstrated the presence of a serous carcinoma component. However, the images that were available for review were more consistent with endometrioid-type tumors. In addition, these 3 cases exhibited no TP53 mutations or homozygous deletion, indicating that the histological type was not serous carcinoma. These findings suggest that survival differences between PIK3CA mutated and non-mutated cases may not be attributed to differences in patient age, tumor stage, FIGO grade or histological subtype.

A total of 56 somatic PIK3CA mutations were identified in 48 patients with CNL-EEC, and a subset of these mutated tumors (12.5%; 6/48) contained >1 PIK3CA mutation. PIK3CA mutations occurred predominantly in hotspots centered on p110-α functional domains (Fig. 3), and around 30% (17/56) occurred within exons 1–7, which encode the N-terminal domains of p110-α, including the p85/adaptor-binding domain and the protein kinase-C homology 2 domain. In addition, around 70% (39/56) of PIK3CA mutations occurred within exons 9 and 20, which encode the C-terminal helical and kinase domains (Fig. 3). The majority of cases (79% of patients and 75% of overall mutations) contained mutations implicated in PIK3CA activation and gain-of-function (Table II). The following recurrent activating mutations were also identified: R88Q, R93Q, N345K, C420R, E542K, E545K (most common), Q546P, D939G, M1043V, M1043I, H1047R (second most common) and H1047L (Fig. 3 and Table II). These findings support the hypothesis that endometrial adenocarcinomas possess a unique spectrum of somatic PIK3CA mutations in which a significant number of mutations occur in the amino terminal domain of p110-α compared with other cancer types, such as colorectal, breast or bladder carcinomas (4,9).

Despite its growth-promoting properties, the effect of PIK3CA mutation on patient prognosis varies according to the cancer subtype. In patients with colorectal or lung cancer, mutations of PIK3CA are associated with poor prognosis. By contrast, PIK3CA mutations have been associated with favorable prognosis in patients with breast cancer and esophageal squamous cell carcinomas (19–22). In endometrial cancer patients, the influence of PIK3CA mutations on survival and prognosis has been unclear, as there is data to suggest an association between PIK3CA mutations and both favorable and unfavorable prognoses (23–25).

The TCGA Data Portal on endometrial adenocarcinoma offers a host of tools that can be used to interrogate specific genetic events relative to survival and clinicopathological characteristics, as well as to generate hypotheses for future testing. In the present study, we hypothesized that PIK3CA mutations in EEC may be associated with favorable survival outcomes, possibly specific to a molecularly sub-defined cohort of tumors that exhibit low somatic copy-number alterations and microsatellite stability. The significantly improved overall survival observed in all patients with endometrioid-type adenocarcinomas exhibiting PIK3CA mutations, regardless of the molecular subtype, may reflect the fact that the majority of TCGA tumors were in the CNL-EEC subgroup.

However, due to the limitations of the TCGA study (i.e., small sample size of the CNL-EEC subgroup, relatively short follow-up time, lack of information on co-morbidities), these findings are exploratory and hypothesis-generating in nature, rather than definitive. For this reason, future studies with multivariate analyses and long-term follow-up to determine the effect of other clinical co-variables (including race, body mass index, estrogen receptor/progesterone receptor status, co-morbidities and treatment regimens) on survival outcome are required. In addition, long-term multivariate analyses with increased power are essential to determine the effect of other molecular co-variables. For example, Liang et al (11) previously reported that ARID1A mutations co-occur with PI3K pathway mutations in endometrial cancer and lead to activation of the PI3K signaling pathway. In the TCGA CNL-EEC subgroup, somatic mutations of ARID1A occurred in 42% of cases (38/90) with a trend towards improved overall survival (P=0.0517) and no differences in progression-free survival (P=0.86). By contrast, significantly improved overall survival was observed in cases with PIK3CA-ARID1A co-occurring mutations (P=0.00026), with no differences in progression-free survival (P=0.88; data not shown).

Finally, the mechanism by which PIK3CA mutations affect patient survival and the mechanism that explains why there appears to be no association between PIK3R1 mutations and survival outcome are unclear, as PIK3CA and PIK3R1 are subunits of the same kinase (8,11). One possible explanation for this is that PIK3CA- and PIK3R1-mutated tumors may have different driver mutations.

In conclusion, the results presented in the current study suggest that PIK3CA mutations may serve as a favorable prognostic biomarker in EEC, depending on further molecular sub-stratification of the tumors. Therefore, future studies on larger independent cohorts with long term follow-up are warranted to further analyze this association and to validate the findings of the TCGA project.