¹¹C-Choline PET/CT in castration-resistant prostate cancer patients treated with docetaxel

To investigate the role of ¹¹C-choline PET/CT for evaluating the response to treatment in patients with metastatic castration-resistant prostate cancer (mCRPC) treated with docetaxel in comparison with PSA response.

Inclusion criteria were (a) proven mCRPC, (b) docetaxel as first line of chemotherapy (docetaxel 75 mg/m² + prednisone 5 mg), and (c) ¹¹C-choline PET/CT and PSA values assessed before and after docetaxel administration. A total of 61 patients were retrospectively enrolled (mean age 68.9 years, range 57 – 84 years). ¹¹C-Choline PET/CT was performed at baseline before docetaxel treatment (PET1) and after the end of treatment (PET2). PSA values were measured before treatment (PSA1) and after treatment (PSA2). PET2 was reported as complete response (CR), partial response (PR) or stable disease (SD). Progressive disease (PD) was considered if a new lesion was seen. PSA trend was calculated from the change in absolute values between PSA1 and PSA2. A decrease of ≥50 % between PSA1 and PSA2 was considered a PSA response. Clinical, radiological and laboratory follow-up ranged from 6 to 53 months (mean 13.5 months).

Of the 61 patients, 40 (65.5 %) showed PD on PET2, 13 (21.3 %) showed SD, 2 (3.4 %) showed PR, and 6 (9.8 %) showed CR. An increasing PSA trend was seen in 29 patients (47.5 %) and a decreasing PSA trend in 32 patients (52.5 %). A PSA response of ≥50 % was seen in 25 patients (41 %). Radiological PD was seen in 23 of the 29 patients (79.3 %) with an increasing PSA trend, in 16 of the 32 patients (50 %) with a decreasing PSA trend, and in 11 of the 25 patients (44 %) with a PSA response of ≥50 %. In the multivariate statistical analysis, the presence of more than ten bone lesions detected on PET1 was significantly associated with an increased probability of PD on PET2. No association was observed between PSA level and PD on PET2.

Our results suggest that an increasing PSA trend measured after docetaxel treatment could be considered predictive of PD. In patients with decreasing PSA values (decreasing PSA trend and a PSA response of ≥50 %), ¹¹C-choline PET/CT may be useful to identify those with radiological progression despite a PSA response. Finally, the tumour burden, expressed as number of bone lesions on PET1, is significantly associated with an increased probability of PD on PET2.