The Gleason score (GS) of prostate cancer on diagnostic biopsies is an important
parameter for therapeutic decision-making. Biopsy GS under-estimates the actual GS at
radical prostatectomy in a significant number of patients due to sampling artifact. The
aim of this study was to identify markers that are differentially expressed in Gleason
grade 3 (GG3) tumor glands embedded in GS 4 + 3 = 7 and GS 3 + 3 = 6 prostate
cancer using laser capture microdissection and RNA sequencing.
GG3 tumor glands embedded in nine GS 3 + 3 = 6 and nine GS 4 + 3 = 7 prostate
cancers were isolated by laser capture microdissection of frozen radical prostatectomy
specimens. After RNA amplification and RNA sequencing, differentially expressed genes
in both GG3 components were identified by a 2log fold change > 1.0 and p-value < 0.05.
We applied immunohistochemistry on a tissue micro-array representing 481 radical
prostatectomy samples for further validation on protein level.
A total of 501 genes were up-regulated and 421 down-regulated in GG3 glands
embedded in GS 4 + 3 = 7 as compared to GS 3 + 3 = 6 prostate cancer. We selected
HELLS, ZIC2 and ZIC5 genes for further validation. ZIC5 mRNA was up-regulated 17 fold
(p = 8.4E–07), ZIC2 8 fold (p = 1.3E–05) and HELLS 2 fold (p = 0.006) in GG3 glands
derived from GS 4 + 3 = 7. HELLS expression of ≥ 1% occurred in 10% GS < 7, 17% GS 7
and 43% GS >7 prostate cancer (p < 0.001). Using a cut-off of ≥ 1%, protein expression
of ZIC5 was present in 28% GS 7 cancer (p < 0.001).
ZIC2 was neither associated with GS nor outcome in our validation set. HELLS was
independently predictive for biochemical-recurrence after radical prostatectomy
(HR 2.3; CI 1.5–3.6; p < 0.01).
In conclusion, HELLS and ZIC5 might be promising candidate markers for selection
of biopsy GS 6 prostate cancer being at risk for up-grading at prostatectomy
