Refined cut-off for TP53 immunohistochemistry improves prediction of TP53 mutation status in ovarian mucinous tumors: implications for outcome analyses

Abstract

TP53 mutations are implicated in the progression of mucinous borderline tumors (MBOT) to mucinous ovarian carcinomas (MOC). Optimized immunohistochemistry (IHC) for TP53 has been established as a proxy for the TP53 mutation status in other ovarian tumor types. We aimed to confirm the ability of TP53 IHC to predict TP53 mutation status in ovarian mucinous tumors and to evaluate the association of TP53 mutation status with survival among patients with MBOT and MOC. Tumor tissue from an initial cohort of 113 women with MBOT/MOC was stained with optimized IHC for TP53 using tissue microarrays (75.2%) or full sections (24.8%) and interpreted using established criteria as normal or abnormal (overexpression, complete absence, or cytoplasmic). Cases were considered concordant if abnormal IHC staining predicted deleterious TP53 mutations. Discordant tissue microarray cases were re-evaluated on full sections and interpretational criteria were refined. The initial cohort was expanded to a total of 165 MBOT and 424 MOC for the examination of the association of survival with TP53 mutation status, assessed either by TP53 IHC and/or sequencing. Initially, 82/113 (72.6%) cases were concordant using the established criteria. Refined criteria for overexpression to account for intratumoral heterogeneity and terminal differentiation improved concordance to 93.8% (106/113). In the expanded cohort, 19.4% (32/165) of MBOT showed evidence for TP53 mutation and this was associated with a higher risk of recurrence, disease-specific death, and all-cause mortality (overall survival: HR = 4.6, 95% CI 1.5-14.3, p = 0.0087). Within MOC, 61.1% (259/424) harbored a TP53 mutation, but this was not associated with survival (overall survival, p = 0.77). TP53 IHC is an accurate proxy for TP53 mutation status with refined interpretation criteria accounting for intratumoral heterogeneity and terminal differentiation in ovarian mucinous tumors. TP53 mutation status is an important biomarker to identify MBOT with a higher risk of mortality.

Figure 1.. TP53 immunohistochemistry staining patterns.

A. Normal pattern with heterogeneous nuclear staining in variable distribution. B. Abnormal overexpression (OE) with virtually all viable tumor cell nuclei showing strong nuclear staining. C. Abnormal complete absence with no nuclear staining of tumor cells but normal control staining in non-tumor stromal or immune cells. D. Abnormal cytoplasmic staining with unequivocal cytoplasmic staining and variable nuclear staining. E. Mucinous borderline tumor with intratumoral heterogeneity or subclonal TP53 abnormal pattern. Inset: both normal (upper) and abnormal OE patterns (lower) are seen within the same tumor. Abnormal OE is seen in an area of mucinous intraepithelial carcinoma. In addition, abnormal OE area displays terminal differentiation with the basal layer of cells demonstrating abnormal OE pattern staining with sparing of superficial areas.

Figure 2.. TP53 immunohistochemistry and TP53 mutations by sequencing in ovarian mucinous tumors.

Ovarian mucinous tumors with variable percentages of TP53 overexpression: A. 5% overexpression or > 12 consecutive strongly staining cells. B. 50% overexpression. C. 70% overexpression. D. 100% overexpression. E. Concordance between mutation status by sequencing and immunohistochemistry improved with application of refined (minimum 5% abnormal OE pattern) instead of established criteria, with improvements observed in cases with splicing and missense mutations. F. The percentage of tumor cells overexpressing TP53 in mucinous borderline tumors (MBOT) and carcinomas (MOC) (median 35% and N=11 in MBOT; median 60% and N=69 in MOC; p=0.040). G. TP53 mutation allele frequencies in MBOT and MOC (median 0.44 and 0.55 respectively; p=0.38).

Figure 3.. Kaplan-Meier survival plots of ovarian mucinous borderline tumors (MBOT) and mucinous carcinomas (MOC) stratified by TP53 status using mutation and immunohistochemistry data.

A, C, E. Progression-free (PFS; A), overall (OS; C), and disease-specific (DSS; E) survival in patients with MBOT. B, D, F. Progression-free (B), overall (D), and disease-specific (F) survival in patients with MOC.