Impact of the tumor microenvironment in splenic metastasis in high-grade serous ovarian cancer revealed by quantitative proteomics

Objectives: High grade serous ovarian cancer (HGSOC) patients often present with diffuse metastatic spread at diagnosis which correlates with poor prognosis. The relationship between tumor cell metastasis and the microenvironment remains poorly understood. Our study is focused on defining proteome profiles in tumor and stroma cell populations in primary and malignant tumors to improve our understanding of molecular profiles underlying metastatic spread.

Methods: A quantitative mass spectrometry-based proteomic analysis was performed on laser microdissected (LMD) tumor and stroma cell populations from primary HGSOC tumors along with patient matched metastases from the liver, peritoneum, omentum, and spleen for 32 patients. Unique and selective proteome alterations in splenic metastases were validated from an independent analysis of LMD enriched tumor and stroma from 13 HGSOC patients.

Results: We quantified >7,400 and >5,600 proteins from tumor and tumor-involved stroma collections, respectively, and unsupervised analyses showed that tumor cells cluster by patient while stromal cells largely by organ site (K-S p < 2.2e-16). A differential analysis showed that metastatic tumor cells from the spleen exhibited more uniquely altered proteins compared the omentum or liver, among which fourteen splenic-specific tumor cell proteins were validated in an independent set of LMD enriched primary (n=12) and splenic (n=6) tumor cell specimens (Spearman Rho = 0.793). Comparison of tumor-involved stroma collections from patient matched primary and splenic metastases identified 132 altered proteins that were highly correlated between these cohorts (Spearman Rho = 0.883, P<0.01). Comparison of tumor-involved stromal proteomes with benign spleen identified 30 proteins uniquely elevated in tumor-involved stroma from splenic metastases.

Conclusions: Our study identified that proteome profiles of HGSOC tumor cells are highly conserved by patient while tumor-involved stroma correlates more with disease site. We also identified highly conserved protein alterations in primary and splenic metastasis in HGSOC patients, including a subset of features reflecting tumor-involved stroma in the spleen. These findings support improved molecular characterization of the tumor microenvironment with HGSOC.