Background: Metastatic squamous cell penile carcinoma (mSCPC) is an orphan disease with a virally induced oncogenesis. PD-L1 expression rate is around 60% with a strong correlation between PD-L1 in the primary tumour and metastases. The first line systemic treatment relies on platinum-based chemotherapies with a median progression free survival and overall survival around 7.5 and 16 months (mo), respectively. Immunotherapies targeting PD-1/PD-L1 axis are effective in other squamous cell or HPV related cancers. Methods: PULSE is a national prospective multicenter open label single arm phase II trial. Thirty-two pts will be enrolled after a radiological assessment showing a non-progressive disease after 3 to 6 cycles of a first line platinum-based polychemotherapy. Pts will receive AVE injections 10mg/kg every two weeks until progression or unacceptable toxicity. The primary endpoint will be the progression free survival (PFS) from AVE initiation according to RECIST v1.1 criteria. Key secondary endpoints will include, overall survival, safety. Here we report the results of the first interim analysis (IA). Results: From September 2019 to October 2022, 14 pts has been enrolled. Within the 9 first patients involved for the IA the median age was 69.9 years; 89% of pts had an ECOG 0-1. Of them, 1 patient and 8 pts had stage 3 and 4 disease at chemotherapy initiation, respectively. Median follow-up was 5.8 [2.3-17.2] mo. Chemotherapy regimens were triplets for 5 pts (56%), containing cisplatin for 56% and a taxane for all pts. Median duration of chemotherapy was 3.7 mo [1.2; 11.7]. At AVE initiation, 5 pts (56%) had partial or complete response and 4 pts (44%) had stable disease. Median duration of AVE was 3.7 mo with a majority (83%) of discontinuation linked to disease progression. Survival data are shown in the table. No new safety signal was identified. Conclusions: PULSE is the first prospective trial exploring avelumab maintenance activity in mSCPC. After the IA the DSMB have recommended to pursue the study based on these promising results. Updated results with additional patients, longer follow-up and ancillary explorations with biomarkers analysis will be presented at the meeting. Clinical trial information: NCT03774901.