ASCO 2017: Results of LATITUDE: ADT with Abiraterone Acetate Plus Prednisone in High-Risk Metastatic Hormone-Naive Prostate Cancer

Chicago, IL ( Dr. Karim Fizazi and colleagues presented their much-anticipated results from the LATITUDE trial at the 2017 ASCO annual meeting’s plenary session. In a phase III, double-blind, randomized setting, LATITUDE tested androgen deprivation therapy (ADT) with abiraterone acetate (AA) plus prednisone vs ADT + placebo in newly diagnosed high-risk metastatic hormone-naïve prostate cancer patients.

The de novo metastatic prostate cancer global incidence is striking: 3% in the US and rising, 6% across Europe, 4-10% in Latin America, and nearly 60% in Asia-Pacific. Historically, ADT has been the standard of care, however, most men with metastases progress to metastatic castration-resistant prostate cancer (mCRPC) driven by the reactivation of AR signaling. As Dr. Fizazi notes, ADT + docetaxel is the new standard of care for men with metastatic hormone naïve disease (with high disease burden) based off of 3 recent RCTs: GETUG-15,1 CHAARTED,2 and STAMPEDE.3 As Dr. Fizazi mentioned, the rationale for adding AA + prednisone to ADT for metastatic hormone-naïve prostate cancer patients is threefold: (i) the mechanism of resistance to ADT may develop early, (ii) ADT alone does not inhibit androgen synthesis by the adrenal glands or prostate cancer cells, and (iii) AA + prednisone improves overall survival (OS) in mCRPC patients and reduces tumor burden in high-risk, localized prostate cancer. These points suggest that there is a role for inhibiting extragonadal androgen synthesis prior to the development of castration resistance. 

The objectives of LATITUDE were to evaluate the addition of AA + prednisone to ADT on clinical benefit in men with newly diagnosed, high-risk, metastatic hormone-naïve prostate cancer. High-risk was defined as meeting at least two of three criteria: (i) Gleason score ≥8, (ii) presence of ≥3 lesions on bone scan, (iii) presence of measurable visceral lesions. Patients were stratified by the presence of visceral disease (yes/no) and ECOG performance status (0, 1 vs 2) and then randomized 1:1 to either ADT + AA (1000 mg daily) + prednisone (5 mg) (n=597) or ADT + placebo (n=602). The co-primary endpoints were overall survival (OS) and radiographic progression-free survival (rPFS). Secondary endpoints included time to: (i) pain progression, (ii) PSA progression, (iii) next symptomatic skeletal event, (iv) chemotherapy, and (v) subsequent prostate cancer therapy. The study was conducted at 235 sites in 34 countries in Europe, Asia-Pacific, Latin America, and Canada. Dr. Fizazi notes that the study was designed and fully enrolled prior to publication of the CHAARTED2 and STAMPEDE3 results. For rPFS, with an alpha of 0.001 and power of 94%, 565 events (single analysis) were needed to detect an HR of 0.67. For OS, at an alpha of 0.049 and power of 85%, 426, 554, 852 (2 interims, 1 final analysis) events were needed to detect an HR of 0.81. The results presented in this session were from the first interim analysis. 

The treatment arms were well balanced, with >95% of patients presenting with ≥3 bone metastases at the screening in both arms. Over a median follow-up of 30.4 months, patients treated with ADT + AA + prednisone had a 38% risk reduction of death (HR 0.62, 95%CI 0.51-0.76) compared to ADT + placebo. Median OS was not yet reached in the ADT + AA + prednisone arm compared to 34.7 months in the ADT + placebo arm. OS rates at 3 years for the ADT + AA + prednisone arm was 66%, compared to 49% in the ADT + placebo arm. This OS benefit was consistently favorable across all subgroups including ECOG 0 and 1-2, visceral metastases, Gleason ≥8 disease, and bone lesions >10. Second, there was also 53% risk of reduction of radiographic progression or death for patients treated with ADT + AA + prednisone (median 33.0 months; HR 0.47, 95%CI 0.39-0.55) compared to ADT + placebo (14.8 months). Third, there was statistically significant improvement across all secondary endpoints for ADT + AA + prednisone: (i) time to PSA progression (HR 0.30, 95%CI 0.26-0.35), (ii) time to pain progression (HR 0.70, 95%CI 0.58-0.83), (iii) time to next symptomatic skeletal event (HR 0.70, 95%CI 0.54-0.92), (iv) time to chemotherapy (HR 0.44, 95%CI 0.35-0.56), and (v) and time to subsequent prostate cancer therapy (HR 0.42, 95%CI 0.35-0.50). Secondary to the above results, the study was discontinued after the first interim analysis. Adverse events were comparable in the two groups. Hypertension only rarely required treatment discontinuation, and only two patients discontinued treatment due to hypokalemia (no hypokalemia-related deaths). Two patients in each arm died of cerebrovascular events, and 10 patients treated with ADT + AA + prednisone compared to 6 patients treated with ADT + placebo died of cardiac disorders.

In conclusion, the phase III LATITUDE study demonstrated that ADT + AA + prednisone leads to a significantly improved OS with a 38% reduction in risk of death, significantly prolonged rPFS (53% reduction), and improvement across all secondary endpoints. The overall safety profile was consistent with the AA + prednisone mCRPC trials. Based on these findings, Dr. Fizazi states “the addition of AA + prednisone to ADT can potentially be considered a new standard of care for patients with high-risk, newly diagnosed hormone-naïve prostate cancer.” The full manuscript was subsequently published in the New England Journal of Medicine at the conclusion of this plenary session.

Presented by: Karim Fizazi, MD, Ph.D., Head of the Department of Cancer Medicine at the Institut Gustave Roussy, Villejuif, France and Professor of Oncology at the University of Paris

Written by: Zachary Klaassen, MD, Urologic Oncology Fellow, University of Toronto, Princess Margaret Cancer Centre, Twitter: @zklaassen_md at the 2017 ASCO Annual Meeting - June 2 - 6, 2017 - Chicago, Illinois, USA