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46 Background: Bone is frequently involved in metastatic hormone sensitive prostate cancer (mHSPC). Whole-body diffusion-weighted magnetic resonance imaging (WB-DW-MRI) is a promising imaging technique for the assessment of bone response in prostate cancer. It is not known whether the addition of antiresorptive agents can improve disease response in bone in mHSPC patients undergoing next generation hormonal agents. Methods: In this multicenter phase II study patients with de novo or relapsed mHSPC and bone metastases at bone scan were randomly allocated with a 1:1 ratio to receive either androgen deprivation therapy (ADT) plus Enzalutamide (E arm) or the same combination with the addition of Zoledronic Acid (EZ arm). The study was designed to observe a significant increase in bone response rate in the experimental arm after 12 months of treatment, as assessed through WB-DW-MRI. WB-DW-MRI was performed centrally at baseline and after 6 and 12 months and images were evaluated by the same radiologist. Results: From February 2018 to June 2021, 126 mHSPC patients were randomized, 64 in EZ arm and 62 in E arm. A total of 111 patients, 54 from E arm and 57 from EZ arm, were eligible for WB-DW-MRI assessment (15 patients were excluded because of the absence of bone target lesions at MRI or specific contraindications to MRI). Bone response at 6 months was observed in 41 patients (76%) in E arm and 41 patients (72%) in EZ arm; the corresponding bone response at 12 months were 44 (82%) and 44 (77%), respectively (OR 0.77; 95%IC 0.30-1.93; p = 0.6). Complete response was the best overall bone response after 12 months in 9 patients (17%) from E arm and in 11 patients (19%) from EZ arm. In the same period, treatment was interrupted due to disease progression in 7 (13%) and 7 (12%) patients in E and EZ arm, respectively. Conclusions: The addition of Zoledronic Acid to Enzalutamide and ADT did not improve bone disease response in patients with mHSPC. WB-DW-MRI was able to detect bone responses in a great proportion of patients. Clinical trial information: NCT03336983 .

435 Background: Targeted therapies (TT) improved survival in mRCC but treatment-related toxicities may worsen quality of life and lead to treatment discontinuation. AS is a feasible strategy in pts with indolent disease but effects on tumor burden (TB) and prognosis have not been investigated. Methods: In this retrospective study we included pts who received AS at our centre. The TB, defined as the number of sites of disease, was collected with the IMDC class, just before and after AS. The time on surveillance (ToS) was defined as the time from the start of AS to the beginning of therapy or last follow-up. The OSs were collected from the start of AS or TT. Results: 48 pts started AS from January 2007 to April 2016. After a median follow up of 37.3 months, 79.2% are still alive. At baseline the main sites of metastases were: lung (56%), nodes (25%), pancreas (14%), adrenal gland (8%), CNS (8%), and bone (6%). TB was one site in 65 %, two in 31%, and >2 sites in 4%. The IMDC prognostic class was favorable in 68,8%, intermediate in 25%, and poor in 6.3% of pts. After a median ToS of 16.7 months (95% CI 9.6-23.7), 34 patients (70.8%) started a TT, only 1/24 patient had progression as the best response. Significant difference in ToS were found where pts with good (19.9 mos) or intermediate (17.7 mos) class were compared to the poor group (5.2 months) (p2 sites in 18%; and 14 pts had new sites of disease. The IMDC class changed in four patients from good to intermediate. The median OSs was not reached from the start of surveillance and was 64.4 months from the start of TT. Conclusions: AS is an option for management of mRCC pts with good and intermediate prognosis. AS allows to delay the start of TT avoiding toxicity and worsening quality of life. Despite the fact pts in AS have increased TB and rarely a worsening of prognostic class, the survival remains longer and the effectiveness of subsequent therapy seems not to be affected.

525 Background: Sunitinib (S) is a standard first line treatment of metastatic renal cell carcinoma (mRCC). Asthenia and fatigue are the most prevalent toxicities but the relevant causes are not fully elucidated. Since endocrine glands are highly vascularized, the potent antiangiogenic effect of S can potentially impair their function. With the exception of hypothyroidism, the endocrine-related side-effects of S have not been extensively explored. Methods: We performed a cross-sectional study in which pituitary, thyroid, parathyroid, adrenal and gonadal functions were assessed in 25 mRCC patients who received 9 months of S therapy. Since a high prevalence of hypogonadism was observed, we subsequently enrolled 16 mRCC male patients in a prospective cohort study in which serum testosterone (T) serum free T, serum FSH and LH were evaluated at baseline and after 6 weeks (1 cycle) of S therapy. In patients eligible for testosterone replacement after andrologic evaluation, a FACT-G questionnaire for quality of life (QoL) assessment was prospectively administered at baseline and after 3 months. Results: In the cross sectional study 15/22 S treated male patients (68%) had serum T below the normal range and 13 of them (87%) presented with low/normal levels of LH. In the prospective study mean T levels (95% CI) were 5.04 ng/ml (3.4 - 6.7) at baseline and 4.1 ng/ml (3 - 5.3) after 6 weeks (p 0.05). The corresponding free T were 91.4 pg/ml (66 – 116.8) and 80.2 pg/ml (65 – 95.3) (p 0.24), respectively. Hypogonadism was observed in 5 (31%) patients at baseline and 10 (63%) patients after 6 weeks of S therapy. In the 5 patients becoming hypogonadic after S therapy, LH was 11.4 mU/ml (3.2 - 19.5) at baseline and 11.5 mUI/ml (0 – 23.5) after 6 weeks. Four patients were addressed to testosterone replacement. QoL significantly improved in 3 of them, with the strongest advantage in the physical comfort area. Conclusions: S therapy induces hypogonadism in a high proportion of male patients with mRCC. Low or inappropriately normal LH levels are consistent with a pituitary origin of the endocrine disorder. Testosterone replacement may improve the QoL and treatment tolerance.

175 Background: Abiraterone acetate (AA) deeply inhibits androgen synthesis but leads to an ACTH driven increase in mineralocorticoid hormones requiring glucocorticoid supplementation that may impair its antineoplastic efficacy. New strategies for the management of the AA induced mineral corticoid excess syndrome (MCES) are warranted. Methods: We analyzed in vitro the interaction in terms of proliferative activity of AA plus/minus prednisone with the steroid aldosterone receptor antagonists: eplerenone, spironolactone, a non-steroidal aldosterone receptor antagonist (PF-03882845) and the epithelial sodium channel antagonist amiloride. LNCaP were grown in a medium with charcoal-treated serum and concentration-response curves for each studied drug were performed. Besides, the activity of amiloride plus hydrochlorothiazide was assessed in the clinical management of AA induced MCES in 5 consecutive patients with castrate resistant prostate cancer. The recovery of AA induced MCES symptoms and signs was the primary end point. Results: Prednisone, spironolactone and eplerenone induced an increase in the LNCAP proliferation rate and antagonized the AA-induced reduction of the cell proliferation in a concentration-dependent manner, while PF-03882845 did not. Amiloride at high concentrations induced cell death. When combined with AA +/- prednisone, amiloride at low concentration did not interfere with AA anti-proliferative activity however an additive inhibitory effect was observed at higher concentrations. The association of amiloride with hydrochlorothiazide led to a complete disappearance of all clinical and biochemical signs of abiraterone induced MCES in the 5 treated patients. Conclusions: Amiloride and PF-03882845 do not negatively interfere with the AA inhibition of proliferative activity of prostate cancer cells in vitro. The association of amiloride plus hydrochlorothiazide is efficacious in the management AA induced MCES.