A valuable pair - candidate biomarkers RBM3 and PODXL in urothelial bladder cancer

Abstract: Bladder cancer is a heterogenous disease, ranging from minimally invasive, low-grade tumours with low
recurrence rates and mortality on one end of the spectrum, and muscle invasive, high-grade disease prone to
recurrence, progression and death at the other end.
The aim of this thesis was to investigate the expression, clinicopathological correlates and prognostic significance
of the candidate biomarkers podocalyxin-like protein (PODXL, papers II and III) and RNA-binding motif protein 3
(RBM3, papers I, III and IV) in urothelial bladder cancer (UBC). In paper IV, the potential predictive significance of
RBM3 was also examined. The candidate biomarkers were examined alongside established clinical risk factors.
RBM3 expression was evaluated by immunohistochemistry in tissue microarrays (TMA) from three different
patient cohorts (n=343 in paper I, n=272 in paper III and n=151 in paper IV). In paper I, negative RBM3 expression
was significantly associated with unfavourable tumour characteristics and was an independent predictor of shorter
disease-specific survival (DSS) as well as 5-year overall survial (OS). Patients with Ta/T1 tumours displaying
negative RBM3 expression had a significantly reduced 24 month progression-free survival (PFS) and 5-year OS.
No association was seen between RBM3 expression and recurrence. In paper 3, these associations were
validated, although with a somewhat different cut-off. Low RBM3 expression was significantly associated with
unfavourable tumour characteristics and was an independent predictor of a shorter OS in both the full cohort and
in T1 disease.
In paper IV, the expression of RBM3 was evaluated in tumours from 151 patients treated with cystectomy due to
muscle-invasive UBC, 45.7% of which had received neoadjuvant chemotherapy (NAC). RBM3 expression was not
prognostic in the full cohort. However, when accounting for NAC, there was a significantly reduced RFS in in the
group of patients with high RBM3 expression who had not been treated compared to those that had received NAC
(p=0.044). The association between high RBM3 expression and response to chemotherapy was strengthened by
the silencing of RBM3 in UBC cell lines, rendering them less sensitive to cisplatin and gemcitabine.
PODXL expressed in the cell membrane was evaluated by immunohistochemistry in TMA from three different
patient cohorts (n=100 and n=343 in paper II and n=272 in paper III). Membranous expression of PODXL was
strongly and significantly associated with unfavourable tumour characteristics in all three cohorts. In paper II,
PODXL independently predicted a shorter DSS and OS in the full cohort, and a shorter PFS and DSS in patients
with Ta/T1 tumours. In paper III, membranous PODXL expression was significantly associated with a shorter OS
in both the full cohort and T1 tumours, but not independent of other prognostic factors.
The conclusions drawn from these studies are that both RBM3 and PODXL are potentially clinically useful
biomarkers in UBC. RBM3 may have clinical implications in NMIBC for decision making in the pre-cystectomy
setting and for its predictive value in patients under consideration for NAC. PODXL is associated with an adverse
prognosis, making it a potentially useful prognostic biomarker. Both candidate biomarkers show great promise,
although their value should be further examined in a prospective setting.