Polo-like kinase 3 and phosphoT273 caspase-8 are associated with improved local tumor control and survival in patients with anal carcinoma treated with concomitant chemoradiotherapy

Abstract

We have recently shown that caspase-8 is a new substrate of Polo-like kinase 3 (Plk3) that phosphorylates the protein on residue T273 thereby promoting its pro-apoptotic function. In the present study we aimed to investigate the clinical relevance of Plk3 expression and phosphorylation of caspase-8 at T273 in patients with anal squamous cell carcinoma (SSC) treated with 5-fluorouracil and mitomycin C-based chemoradiotherapy (CRT). Immunohistochemical detection of the markers was performed in pretreatment biopsy specimens of 95 patients and was correlated with clinical/histopathologic characteristics including HPV-16 virus load/p16INK4a expression and cumulative incidence of local and distant failure, cancer specific survival (CSS), and overall survival (OS). We observed significant positive correlations between Plk3 expression, pT273 caspase-8 signal, and levels of HPV-16 virus DNA load/p16INK4a detection. Patients with high scores of Plk3 and pT273 caspase-8 showed increased local control (p = 0.011; p = 0.001), increased CSS (p = 0.011; p = 0.013) and OS (p = 0.024; p = 0.001), while the levels of pT273 caspase-8 were significantly associated (p = 0.033) with distant metastases. In multivariate analyses Plk3 expression remained significant for local failure (p = 0.018), CSS (p = 0.016) and OS (p = 0.023). Moreover, a combined HPV16 DNA load and Plk3 or pT273 caspase-8 variable revealed a significant correlation to decreased local failure (p = 0.001; p = 0.009), increased CSS (p = 0.016; p = 0.023) and OS (p = 0.003; p = 0.003). In conclusion these data indicate that elevated levels of Plk3 and pT273 caspase-8 are correlated with favorable clinical outcome in patients with anal SCC treated with concomitant CRT.

Keywords: anal carcinoma; caspase-8; chemoradiotherapy; local control; Polo-like kinase 3.

Figure 1. Immunohistochemical staining of Plk3 and pT273 caspase-8

Examples of anal cancer biopsies with high (A, C) and low (B, D) immunohistochemical detection of Plk3 and pT273 caspase-8. Original magnification × 100 (inlets × 400), scale bar: 100 μm.

Figure 2. Incidence of locoregional and distant failure according to Plk3 and pT273 caspase-8 expression

Cumulative incidence of locoregional (A–B) and distant failure (C–D) according to low Plk3 expression (individual WS ≤ 6) and pT273 caspase-8 levels (≤ median) vs. high Plk3 expression (WS > 6) and high pT273 caspase-8 levels (> median) in pretreatment biopsies of patients with anal carcinoma treated with definitive CRT.

Figure 3. Cancer-specific and overall survival according to Plk3 and pT273 caspase-8 expression

Cancer-specific (A–B) and overall survival (C–D) according to low Plk3 detection (WS ≤ 6) and low pT273 caspase-8 levels (≤ median) vs. high Plk3 detection (WS > 6) and high pT273 caspase-8 Levels (> median) in pretreatment biopsies of patients with anal carcinoma treated with definitive CRT.

Figure 4. Incidence of locoregional and distant failure, CSS and OS according to combined HPV16 DNA load and Plk3 expression

Cumulative incidence of locoregional. (A) and distant failure (B), CSS (C) and OS (D) according to combined HPV16 DNA load and Plk3 detection (high HPV16 DNA load and high Plk3 vs. high HPV16 DNA load and low Plk3 vs. low HPV16 DNA load and low Plk3 expression) in pretreatment biopsies of patients with anal carcinoma treated with definitive CRT.

Figure 5. Incidence of locoregional and distant failure, CSS and OS according to combined HPV16 DNA load and pT273 caspase-8 expression

Cumulative incidence of locoregional. (A) and distant failure (B), CSS (C) and OS (D) according to combined HPV16 DNA load and pT273 caspase-8 levels (high HPV16 DNA load and high pT273 caspase-8 vs. high HPV16 DNA load and low pT273 caspase-8 vs. low HPV16 DNA load and low pT273 caspase-8) in pretreatment biopsies of patients with anal carcinoma treated with definitive CRT.