Size and SUVmax define the contribution of nodal metastases to PSA in oligorecurrent prostate cancer

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Abstract Background To evaluate how prostate‐specific antigen (PSA) levels decrease after removal of isolated prostate cancer (PCa) nodal metastases in relation to their diameter/volume (“PSA‐density of PCa‐metastases”) and maximum standardized uptake value (SUVmax). Methods A total of 83 consecutive patients with solitary nodal recurrence after radical prostatectomy who underwent prostate‐specific membrane antigen‐radioguided salvage surgery were retrospectively analyzed. Using multivariable linear regression models, the PSA‐decrease after removal of each PCa‐metastases (=PSA‐contribution of each PCa‐metastases) was correlated with the long axis diameter/estimated volume and the SUVmax of each removed metastasis. Sizes were measured by imaging and histopathologic examination. Results A total of 83 patients were included with a median (interquartile range [IQR]) PSA‐decrease of 0.56 [0.22, 1.31] ng/mL after salvage surgery. The median [IQR] long axis diameters in imaging and histopathological examination were 8.0 [6.0, 11.0] mm and 8.4 [5.5, 11.1] mm, respectively. The median [IQR] estimated volumes were 0.13 [0.05, 0.32] cc (imaging) and 0.05 [0.02, 0.17] cc (pathology). In multivariable linear regression analyses, the estimated PSA‐contribution ([95% confidence interval [CI]) of each millimeter of long axis diameter was 0.09 [0.03, 0.14] ng/mL (imaging) or 0.08 [0.03, 0.12] ng/mL (histology). The minimum diameter for biochemical recurrence (PSA ≥ 0.2 ng/mL) was >2.2 mm (imaging) or >2.5 mm (histology). The estimated PSA‐contribution [95% CI] of each cc cancer volume was 1.23 [0.51, 1.94] ng/mL (imaging) or 1.46 [0.40, 2.52] ng/mL (histology). SUVmax as surrogate parameter for tissue composition was associated with increased PSA‐contribution of PCa‐metastases (+0.03–0.05 ng/mL per unit increase). Conclusions The diameter/volume and SUVmax of metastatic tissue correlate with its contribution to PSA levels. Therefore, very small metastases may produce too little PSA for biochemical recurrence.

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