Oligometastatic prostate cancer detects by 18F-Choline (FCH) Positron Emission Tomography (PET)/ Computed Tomography (CT) in patients with PSA levels ≤ 5 ng/mL

Objectives: Oligometastatic disease (OMD) is defined as solitary or few detectable metastatic lesions (<5 metastases) that are usually confined to a single organ. In prostate cancer (PC), OMD can be divided into those with a rising PSA following primary therapy or those with castrate resistant prostate cancer (CRPC) with a rising PSA level. The objective of the study was to assess the ability of FCH PET/CT to detect OMD in patients with early recurrence of disease (PSA &#8804;5 ng/mL), both in those after primary therapy (not undergoing androgen deprivation therapy-ADT) and in subjects with a CRPC (undergoing ADT).

Methods: Between 2010 and 2016, from a single institutional database composed by 1293 patients who underwent FCH PET/CT, 327 patients with PC and PSA levels &#8804;5 ng/mL were selected. The mean (SD) age was 71 (10) years. Gleason score ranged between 5 and 10, being 7 in the majority of patients. All patients were treated with a radical prostatectomy ± lymphadenectomy, followed by radiation treatment in 69 subjects (21.1%). One-hundred twenty-two (37.3%) patients were ongoing ADT at the time of PET/CT, while 205 (62.7%) did not. Mean (SD) PSA at the time of PET/CT was 1.25 (1.14) ng/mL, being inferior/equal to 1 ng/mL in 170 (52%), between 1 and 2 ng/mL in 88 (26.9%) and between 2 and 5 ng/mL in 69 (21.1%) patients. The correlation between continuous variables and categorical data was assessed by t-student test or by ANOVA-test, as appropriate. The association between continuous variables was checked by Chi-square test. P< 0.05 was considered statistically significant.

Results: One-hundred ninety-five (59.6%) patients had a negative FCH PET/CT, while 132 (40.4%) had a positive scan. Of these latter patients, 35 (10.7%) had a significant FCH uptake in the prostatic fossae, 60 (18.3%) in lymph nodes and 37 (11.3%) in bone. PSA levels were significantly different between patients with a positive than those with a negative scan (1.78±1.35 vs. 0.89±0.78 ng/mL; p<0.0001), similarly the difference was reported for patients undergoing ADT or not (both p<0.0001). FCH PET/CT was negative in the majority of patients with a PSA &#8804; 1 ng/mL (126/327; 64.6%), being similar in patients with ongoing ADT and not. Conversely, FCH PET/CT was positive in 35 (41.2%) patients not-undergoing ADT with a PSA &#8804; 1 ng/mL and in 22 (46.8%) subjects undergoing ADT with a PSA between 2 and 5 ng/mL. The most of patients undergoing ADT showed OMD in the lymph nodes (27/122; 22.1%). On the other hand, in patients who did not receive ADT, 25 (12.2%) had a significant FCH uptake in the prostatic fossae, 33 (16.1%) in lymph nodes and 27 (13.1%) in bone.

Conclusion: In patients with early recurrence of PC (PSA &#8804; 5 ng/mL), FCH PET/CT is able to detect OMD in 40.4% of cases. This finding has an important impact on the detection of PC recurrent lesions that could be treated by local therapy to achieve long‐term survival or cure.