Maspin as a Prognostic Marker for Early Stage Colorectal Cancer With Microsatellite Instability

Abstract

Colorectal cancers are among the most common cancers and a leading cause of cancer death. In our pursuit to discover molecular markers for better characterization and precision theranostics of these cancers, we first conducted global deep proteome analyses and identified maspin (serpin B5, peptidase inhibitor 5) as an upregulated protein in tumor tissue. We then validated its expression in a large cohort of 743 patients with colorectal cancers of all stages and found that both cytoplasmic and nuclear expression varied widely between different patients. Comparison with clinicopathological features revealed that maspin expression levels correlate significantly only with mismatch repair (MMR) status but not with other features. To elucidate the prognostic significance of maspin, we analyzed two outcome-annotated cohorts, one of 572 early stage cancer patients and another of 93 late stage cancer patients. Kaplan-Meier survival, univariate, and multivariate analyses revealed that maspin overexpression predicts longer overall and disease-free survival for early stage microsatellite instability (MSI) subtype colorectal cancer, but there is no correlation with survival for patients with early stage cancer of the microsatellite stability (MSS) subtype or late stage cancer. Our study identifies maspin expression as an independent prognostic marker for risk stratification of early stage MSI subtype colorectal cancer and may provide guidance for improved therapeutic management.

Keywords: biomarker; colorectal cancer; maspin; pathology; prognosis; serpin B5.

Figure 1

Deep proteomic analysis of CRC by mass spectrometry. (A) Volcano plot of quantified protein changes from 15 patients. The curved solid line shows the FDR (false discovery rate) horizon of 0.05. The horizontal axis indicates log₂-fold change (FC) of protein abundance (cancer relative to matched benign mucosa). The vertical axis shows –log₁₀ of the t-test p-value. Up-regulated proteins are shown in red and down-regulated proteins are shown in blue. Maspin is highlighted by an arrow. (B) Statistical comparison of maspin protein levels detected by mass spectrometric label-free quantitation (LFQ).

Figure 2

Representative immunohistochemical maspin protein stains showing four different TMA cores. (A) Negative (no protein expression), (B) weakly positive, (C) moderately positive (with several positive nuclei, red arrows), (D) strongly positive staining. Original magnifications: 40× (insets, 400×).

Figure 3

Bar graph of maspin protein expression distribution derived from IHC staining of 743 CRCs. (A) Six-hundred and twenty-eight cases of early stage CRC (stages I or II) and (B) One-hundred and fifteen cases of late stage CRC (stages III or IV). The horizontal axis indicates H-score bins (bin width, 10). The vertical axis indicates the absolute case count for each H-score bin.

Figure 4

Overall survival and disease-free survival analyses of early stage CRCs (stages I and II) stratified by combined maspin protein expression (combined high category defined as cases with both high cytoplasmic and positive nuclear maspin protein expression). All other cases are defined as “low.” (A,B) All early stage CRCs, (C,D) early stage CRCs of only the MSS subtype.

Figure 5

Overall survival and disease-free survival analyses of late stage CRCs (stages III and IV) stratified by combined maspin protein expression. (A,B) All late stage CRCs, (C,D) late stage CRCs of only the MSS.

Figure 6

Overall survival and disease-free survival analyses of early stage MSI subtype CRCs (stages I and II) stratified by maspin protein expression. (A,B) Cytoplasmic expression, (C,D) nuclear expression, and (E,F) combined maspin expression.