Ziel/Aim To immunohistochemically validate the primary tumor PSMA expression in newly diagnosed,
treatment-naïve PCa patients imaged with 68Ga-PSMA PET/CT before radical prostatectomy (RP).
Methodik/Methods 40pts underwent 68Ga-PSMA I&T PET/CT before RP. In each prostate lobe tracer uptake was assessed as
focal or negative. After RP all PT were stained with H&E. IHC staining was performed
to assess the expression of PSMA in both lobes of the prostate. The intensity and
percentage of positively stained cells within tumor foci were reported and transformed
to a 4-point immunoreactive score (IRS) scale. The IRS was also reported for normal
prostate (NP).
Ergebnisse/Results Mean age 66±7yrs (range 53-78), median GSC 7 (7-10), median ISUP risk group 3 (2-5),
median PSA value 11 ng/mL (2-140). In 13 pts LNMs were found in post-op. histology;
5 pts presented with PSMA-avid skeletal lesions highly consistent with BMs. Post-op.
hist-path. work-up revealed bilateral prostate involvement in every pt, however in
18% of them (7/40) the PT was PSMA-PET negative. Overall, 35% of prostate lobes (28/80)
had no focal uptake in PSMA-PET. The IRS score was: 2.42 for tumors located in lobes
with focal 68Ga-PSMA I&T uptake, 2.07 for tumors with no focal uptake, and 1.79 for NP. The IRS
for PSMA-PET PT was not significantly higher than for PSMA-PET negative tumors (p = 0.09),
however it was significantly higher than for NP (p<0.01). Pts with PSMA non-avid PT
had Gl. 7, median ISUP risk group 3 (2-3); median PSA was 6 ng/mL (2-11); 1 pt had
LNMs, none had BMs.
Schlussfolgerungen/Conclusions The level of PSMA expression in the tumors with focal tracer uptake visible on PSMA-PET/CT
imaging was not significantly higher than in the tumors without focal uptake. Hence,
the lack of focal uptake cannot be justified by lower or heterogenous PSMA expression.
Other factors contributing to the intensity of tracer uptake should be searched for,
especially low tumor volume, which may result in partial volume effect. Pts with negative
PT uptake had lower disease stage comparing to pts with focal tracer uptake.
