Abstract
Although the expression of cell signaling proteins is used as prognostic and predictive biomarker, variability of protein levels within tumors is not well studied. We assessed intratumoral heterogeneity of protein expression within primary ovarian cancer. Full-length proteins were extracted from 88 formalin-fixed and paraffin-embedded tissue samples of 13 primary high-grade serous ovarian carcinomas with 5–9 samples each. In addition, 14 samples of normal fallopian tube epithelium served as reference. Quantitative reverse phase protein arrays were used to analyze the expression of 36 cell signaling proteins including HER2, EGFR, PI3K/Akt, and angiogenic pathways as well as 15 activated (phosphorylated) proteins. We found considerable intratumoral heterogeneity in the expression of proteins with a mean coefficient of variation of 25% (range 17–53%). The extent of intratumoral heterogeneity differed between proteins (p<0.005). Interestingly, there were no significant differences in the extent of heterogeneity between phosphorylated and non-phosphorylated proteins. In comparison, we assessed the variation of protein levels amongst tumors from different patients, which revealed a similar mean coefficient of variation of 21% (range 12–48%). Based on hierarchical clustering, samples from the same patient clustered more closely together compared to samples from different patients. However, a clear separation of tumor versus normal tissue by clustering was only achieved when mean expression values of all individual samples per tumor were analyzed. While differential expression of some proteins was detected independently of the sampling method used, the majority of proteins only demonstrated differential expression when mean expression values of multiple samples per tumor were analyzed. Our data indicate that assessment of established and novel cell signaling proteins as diagnostic or prognostic markers may require sampling of serous ovarian cancers at several distinct locations to avoid sampling bias.
Highlights
Ovarian cancer is the second most common gynecological malignancy and the one with the highest mortality in the Western world [1]
Intratumoral Heterogeneity of Protein Levels All 36 proteins analyzed in this study showed considerable intratumoral heterogeneity with a mean coefficient of variation (CV) of 25% (Table 1 and Table S2)
We found considerable intratumoral heterogeneity in the expression of protein biomarkers related to cell signaling pathways in high-grade serous ovarian carcinoma
Summary
Ovarian cancer is the second most common gynecological malignancy and the one with the highest mortality in the Western world [1]. During early stages the disease is mostly asymptomatic and most patients are diagnosed with advanced stages resulting in a poor five-year overall survival rate of less than 40% [2]. Standard treatment for patients with ovarian cancer is surgery followed by platinum and taxane based combination chemotherapy. Most patients show initial response to chemotherapy, the majority subsequently develops resistance and 50–75% of patients relapse within five years [3]. The assessment of cell signaling proteins offers the opportunity to identify potential new drug targets as well as to predict response to treatment and aid in individualized treatment decisions [4]. In order to serve as a biomarker for an optimized targeted therapy approach the identification and quantitative analysis of target structures and/ or respective downstream signaling cascades is of high relevance
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
