Differential treatment response of prostate and metastatic lesions in patients with newly diagnosed metastatic prostate cancer.

Abstract

56 Background: We aimed to evaluate the response of primary tumor to systemic treatment in patients with newly diagnosed mPCa with serial PSMA PET/CT scans. Methods: A total of 43 patients with newly diagnosed mPCa who had significant prostatic PSMA uptake at baseline PSMA PET/CT (bPSMA) and underwent at least one follow-up PSMA PET/CT (fPSMA) after receiving systemic treatment were included in the study. Those who received any definitive treatment at localized stage and those who underwent radiotherapy to prostate before fPSMA were excluded. Prostatic and metastatic PSMA response after systemic treatment was categorized as complete response (CR), partial response (PR), stable disease (SD), or progressive disease (PD) as recommended by guidelines. Discordant behavior between prostate and metastases was defined as the condition when metastatic lesions are responding (CR or PR) to systemic treatment while prostate had progressed or vice versa. CHAARTED criteria was applied to categorize patients according to the volume of metastatic disease. Results: The mean age of patients at bPSMA was 67.7 ± 8.5 years. The median PSA at bPSMA was 31.7 ng/dL (IQR: 11.3 – 106.0). Patient characteristics and treatments are summarized. The median time interval between bPSMA and the first fPSMA was 5.7 months (IQR: 4.6 – 7.5). Nine patients (20.9%) had CR, 25 (58.1%) had PR, 5 (11.6%) had SD and 4 (9.3%) had PD at prostate following systemic treatment. Patients with low-volume disease had prostatic CR twice more commonly than those with high-volume disease (27.3% vs 14.3%). In 6 (13%) cases, a significant PSMA uptake at prostate was detected despite a complete response of all metastatic sites. Discordant treatment responses at the prostate and metastatic sites were observed in 6 out of 43 (16%) patients. Conclusions: Discordant behavior between prostate and metastases are not rare in mPCa. Almost one-fourth of patients with low-volume mPCa achieved a complete prostatic response with systemic treatment only. Prostatic response on PSMA PET/CT following systemic treatment can be used to select ideal patients for the treatment of the primary tumor in patients with mPCa. [Table: see text]