Immunohistochemistry was used to investigate FGFR3 expression levels in 108 ependymal tumor samples applied to TMAs. The TMA cohort (Table
1), representing different grades of ependymomas and disease subtypes, has been partly reported previously [
26]. FGFR3 immunoreactivity was detected in 27 (37%) of the cases; 11 (15%) showed weak immunostaining, 11 (15%) showed moderate immunostaining and 5 (7%) were strongly immunopositive. Increased staining was also observed in pseudorosette structures (Additional file
1: Figure S1b). Recurrent tumors showed typically similar staining levels as the primary tumor. With respect to the association analysis (Additional file
1: Figure S2), FGFR3 staining was significantly associated with a higher tumor grade (
p < 0.01, Fisher’s exact test, Fig.
1b, Table
2). None of the grade I cases showed detectable FGFR3 expression. Moderate-to-strong FGFR3 immunostaining was predominantly detected in cerebral tumors as compared to other locations (
p < 0.001, Fisher’s exact test, Fig.
1c, Table
2). Elevated FGFR3 immunopositivity in high-grade cerebral tumors suggests that FGFR3 immunostaining may be typical for pediatric ependymomas. Indeed, patients with age < 20 years at tumor onset had a higher frequency of FGFR3 immunopositive staining (
p < 0.05, Fisher’s exact test, Fig.
1d). Cases with moderate-to-strong FGFR3 immunostaining tend to show a high proliferation rate (Fig.
1e), although this association was not statistically significant (
p = 0.07, Fisher’s exact test). Importantly, moderate-to-strong FGFR3 immunostaining was significantly associated with shorter overall patient survival (
p < 0.05, log-rank test, Fig.
1f) and shorter time to tumor recurrence (
p < 0.01, log-rank test, Fig.
1g). The association with disease-free survival remained significant after adjustment for tumor location, grade, and proliferation (
p = 0.003, RR = 1.82, 95% CI 1.23–2.68 for FGFR3, other variables not significant in the final equation,
N = 77, stepwise Cox regression), but only tumor location (
p = 0.022, RR = 2.47, 95% CI 1.42–5.34,
N = 77, stepwise Cox regression) was a significant prognostic predictor for disease-specific survival in multifactorial analysis. It is relevant to note the patient numbers (
N = 77) are rather low for multifactorial analysis using four different variables. Still, the obtained results suggest that FGFR3 immunopositivity is associated with more aggressive ependymomas.
Table 2
Samples numbers in FGFR1 low, FGFR1 high, FGFR3 low, and FGFR3 high groups in respect to tumor location, tumor grade and patient age
Tumor location |
Spinal | 37 | 6 | 41 | 2 |
Cerebellar | 21 | 4 | 23 | 5 |
Cerebral | 16 | 20 | 20 | 15 |
p-value | 0.0001 | | 0.0002 | |
Tumor grade |
I | 16 | 2 | 18 | 0 |
II | 50 | 15 | 54 | 14 |
III | 10 | 13 | 14 | 8 |
p-value | 0.002 | | 0.013 | |
Patient age |
< 16 | 22 | 12 | 23 | 12 |
> =16 | 50 | 18 | 61 | 10 |
p-value | 0.15 | | 0.055 | |
As pediatric and adult ependymomas differ in many respects and the age association might influence the observed associations, we analyzed the pediatric and adult sample cohorts independently. Patients that were at least 16 years old were considered as adults according to general practice in Finnish pediatric clinics. There were 35 pediatric and 73 adult samples in our cohort. Moderate-to-strong FGFR3 staining was slightly more common in pediatric than adult samples (34.3% vs 13.7%,
p = 0.055, Fisher’s exact test, Table
2). In pediatric patients, moderate FGFR3 immunostaining was observed in cerebellar (31%,
n = 16) and cerebral (29%,
n = 14) tumors and strong FGFR3 staining only in cerebral tumors (21%,
n = 14), whereas all the spinal cases (
n = 5) were negative for FGFR3 (
p = 0.065, Fisher’s exact test). FGFR3 staining was not associated with tumor grade or proliferation index in pediatric ependymomas. In adults, FGFR3 associations were largely very similar as in the whole sample cohort: stronger FGFR3 staining was associated with tumor grade (
p < 0.01,
n = 73, Fisher’s exact test), tumor location (
p < 0.001,
n = 71, Fisher’s exact test) and there was a close-to-significant association with proliferation index (
p = 0.095,
n = 66, Fisher’s exact test). Prognostic associations were mostly nonsignificant in separate survival analyses in pediatric (
n = 14) and adult (
n = 30) sample cohorts, but this was likely due to low sample count in the analysis, as the trend remain the similar. Of note, when FGFR3 staining was divided into four groups, it was associated with worse disease-specific (
p < 0.01, log-rank test) and disease-free (
p < 0.001, log-rank test) survival in pediatric patients.