Natural history of patients with muscle metastases from renal cell carcinoma: Results of the French national ARTEMIS study.

618 Background: Muscle metastases (MM) are among rare secondary locations in renal cell carcinoma (RCC). Current guidelines do not provide specific advice on the management of these patients. There is a lack of scientific literature on the subject, mainly based on case reports or small retrospective monocentric cohorts. To date, therefore, there remains uncertainty about the clinical history, prognosis, and appropriate management of patients with MM. Methods: ARTEMIS is an ambispective national French multicenter, non-interventional study. It was opened to patients with metastatic RCC who had MM. The study was designed to assess overall survival (OS), progression-free survival (PFS), describe diagnostic and treatment modalities, and treatment-related serious adverse events in case of local treatments (TR-SAEs). Results: Median follow-up was 74.4 months IC95% [38.7-84.1]. The 146 enrolled patients were 73.6% male, with a median age of 57.6 years at diagnosis. They were initially diagnosed with stage IV RCC for 40.4% of them and had a favorable (36.2%), intermediate (45.7%), or poor (18.1%) IMDC risk score at the onset of metastases. Initially, metastases were mainly located in the lungs (55.5%), lymph nodes (26.7%), and bones (24.0%). Patients had a history of partial or total nephrectomy in 78.8% of cases. There were 30.0% of patients with synchronous MM. The median times from initial diagnosis or metastatic status to MM discovery were 25.5 [16.8-35.7] months and 8.4 [5.0-13.5] months, respectively. The majority (69.0%) of MM were discovered on conventional injected CT scans, whereas 8.3% were diagnosed clinically. Survival data are displayed on the table. Thirty-seven (25.3%) patients received local treatment of their MM which consisted of: external radiotherapy (48.6%), surgery (27.0%), cryotherapy (27.0%), stereotactic radiotherapy (5.4%), embolization (2.7%). Among them, local treatments prevented local relapse of MM in 28 patients (75.7%). Local TR-SAEs were seen in two patients (5.4%). Conclusions: ARTEMIS is the largest published cohort describing the disease history of patients with RCC suffering from MM. To our knowledge, this is the first study reporting the diagnostic and treatment modalities, also survival data. Despite its low incidence, the issue of these patients is not so rare in physicians’ practice. This work thus allows a greater understanding of clinical features and treatment of this pathology. [Table: see text]