Nuklearmedizin 2020; 59(02): 160
DOI: 10.1055/s-0040-1708334
Wissenschaftliche Poster
PET, SPECT & Co. III
© Georg Thieme Verlag KG Stuttgart · New York

Heterogenous PSMA expression in primary tumor of prostate cancer as a reason for negative 68 Ga-PSMA PET/CT scan? Immunohistochemical validation of 40 patients undergoing radical prostatectomy

W Cytawa
1   Medical University of Gdansk, Department of Nuclear Medicine, Gdansk
,
S Kircher
2   University Hospital Wuerzburg, Institute of Pathology, Wuerzburg, Wuerzburg
,
C Lapa
3   University Hospital, Augsburg, Department of Nuclear Medicine, Augsburg
,
AK Buck
4   University Hospital Wuerzburg, Department of Nuclear Medicine, Wuerzburg
,
B Brockhuis
1   Medical University of Gdansk, Department of Nuclear Medicine, Gdansk
,
S Weber
5   University Hospital Wuerzburg, Wuerzburg
,
P Hartrampf
4   University Hospital Wuerzburg, Department of Nuclear Medicine, Wuerzburg
› Institutsangaben
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Publikationsdatum:
08. April 2020 (online)

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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.