e17105 Background: Continuous androgen deprivation therapy (ADT) is the standard for patients with hormone sensitive prostate cancer that is metastatic on conventional imaging (mHSPC). In the current era many patients receive more potent therapy with both ADT and an ARPI without (doublet therapy) or with docetaxel (triplet therapy). Several trials are examining de-escalation by stopping the ARPI, introducing a treatment holiday, or treating for a finite duration of systemic therapy. Reports on real world experience of treatment holidays for patients with mHSPC are limited. Methods: Following IRB approval, we identified patients in our hospital system with mHSPC, which was M1b or M1c based on CT or MRI and bone scan, and who received ADT and an ARPI for at least 6 months. We examined stage at diagnosis and prior to doublet therapy, treatment history, and testosterone recovery, and recorded if there was PSA or radiologic progression while on treatment holiday. PSA progression was defined stringently as PSA > 0.2 for those who had undergone prostatectomy, and PSA > 2.0 for those who had not. Radiologic progression was on either PET or conventional imaging. Results: Twenty-seven patients with mHSPC went on treatment holiday from doublet therapy. Median age at diagnosis was 67 (range 52-84). Twenty-one of 27 (78%) patients had synchronous metastatic disease, 6 of 27 (22%) had metachronous metastatic disease, and 17 of 27 (63%) underwent radiotherapy to metastatic sites. Median PSA before starting doublet therapy was 19.72 (range 1.03-176), and all achieved undetectable PSA prior to treatment holiday. Twenty-five of 27 (93%) had bone metastases, and 3 of 27 (11%) had lung metastases. Nineteen of 27 (70%) patients continued off therapy without evidence of progression, with a median follow-up of 27 months (range 4.0-57). Eight of 27 (30%) patients had progression (2 with PSA progression, 4 radiologic progression, and 2 with both), and 72% (95% CI: 47%-86%) remained progression-free at 36 months. Median time to testosterone recovery to > 150 ng/mL was 26 months (95% CI: 8.7, NR). Conclusions: In this real-world data, a subset of patients with metastatic prostate cancer and on treatment holiday from doublet therapy had durable time off therapy and without progression. This included patients with synchronous metastatic disease and with high volume disease. Prospective studies are warranted to evaluate which patients are most likely to have durable time off therapy. Of note, a quarter of those whose cancer progressed during treatment holiday had radiologic progression without PSA progression.
VanderWeele et al. (Thu,) studied this question.