Background: Penile squamous cell carcinoma (PSCC) is an uncommon malignancy which accounts for 2,300 new cases and 400 deaths annually worldwide. However, in low-income countries from South America, Asia and Africa, incidence corresponds to 10-20% of all malignancies in men. Approximately 4% of PSCC patients present with metastatic disease at diagnosis. Also, even if diagnosed in early stages (localized disease), around 30% of patients will recur. No improvements have been achieved over the last three decades in platinum-based chemotherapy, which remains the standard-of-care; objective response rate (ORR), median progression-free survival (PFS) and overall survival (OS) are currently at 20-30%, 3-4 months and 7-15 months, respectively. HPV16 is the most important known risk factor for PSCC. Favorable results have been achieved with Pembrolizumab in other HPV-associated cancers, such as cervical and oropharyngeal cancer. HERCULES (LACOG 0218) aims to evaluate the efficacy of pembrolizumab combined with platinum-based chemotherapy as first-line treatment in advanced PSCC. Methods: HERCULES is a phase 2, single-arm, multicentric trial evaluating patients with histologically proven PSCC and metastatic disease (de novo or recurrent); or recurrent locally advanced disease not amenable to curative-intent therapy; or TanyN3M0 or T4NanyM0 (stage IV – AJCC 8th ed) not amenable to curative-intent therapy. Additional inclusion criteria were ECOG PS 0–1; measurable disease by RECIST 1.1; no prior systemic therapy for recurrent or metastatic disease (however, patients progressing after 12 months of neo/adjuvant chemotherapy completion are allowed). The primary endpoint is ORR up to week 24. Secondary endpoints are OS, PFS, clinical benefit rate, immune related response criteria, quality of life, safety, and predictive biomarkers of response/survival. Eligible subjects receive 5-FU 1000mg/m²/day IV D1-D4, cisplatin 70mg/m² or carboplatin AUC 5 IV D1 plus pembrolizumab 200mg IV D1 at each 3-week (Q3W) dosing cycle for 6 cycles, followed by Pembrolizumab 200mg IV Q3W maintenance. Patients without disease progression are allowed to continue pembrolizumab monotherapy until completing 34 cycles, disease progression or unacceptable toxicity, whichever comes first. Tumor evaluations are performed every 6 weeks until week 24. Sample size was calculated as 33 patients to detect an increase in ORR from 20% to 40% up to week 24 with 78.5% power and considering 10% drop-out. From Aug 2020 to Jul 2022, 33 patients were enrolled in 11 Brazilian research sites. Results are expected in 2023. NCT04224740. Clinical trial information: NCT04224740.