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Introduction Systemic Sclerosis (SSc) is a heterogeneous systemic autoimmune disease, in which distinct disease subsets can be identified with autoantibodies. In a large EUSTAR study including >4,000 SSc patients, anti-RNA polymerase III (anti-RNAP3) was positive in 4.5%, with a distinct clinical phenotype including synchronous cancer and specifically breast cancer (Lazzaroni MG, J Rheum 2017)Noteworthy, one study from Italy (Lazzaroni MG. CER 2020) and another from Japan (Saigusa R. J Dermatol 2016) reported a specific association of silicone breast implants (SBI) with anti-RNAP3 positivity in SSc female patients, raising the possibility of a new clinical association. The aim of the study was to analyze the characteristics of female SSc patients with Silicone Breast Implants (SBI) implanted before disease onset.Material and Methods International case-control study within the EUSTAR network (CP117), including female patients with SBI implanted before SSc onset for any reason (cases) and 2-3 SSc female patients without SBI from the same centres (controls) matched for cutaneous subset, age at onset (±5 years) and disease duration (±2 years).Specifically, data regarding the indication for SBI implantation and rupture (cases) and data on breast cancer (cases and controls) were recorded.Results Among 64 SSc patients with SBI (cases) 76.6% had SBI implanted for cosmetic reasons and 46.9% had dcSSc, with anti-RNAP3+ in 23.4%. Anti-RNAP3+ patients, as compared to anti-RNAP3-, had a tendency toward a higher frequency of documented SBI rupture (8/15 vs 13/49, p:066).As compared to 168 matched controls, SBI patients had higher frequency of anti-RNAP3 (23.4% vs 11.9%, p:0.039, OR 2.22 [95% CI 1.06-4.67]) and breast cancer, but not synchronous breast cancer (table 1). Clinical characteristics were globally similar in cases and controls, except for the lower prevalence of clinically relevant arrythmias in cases. ILD was slightly less frequent in SBI+ (43.8% vs 54.5%), with NSIP being the most frequent pattern in both groups (84.6% in cases and 82.6% in controls).Conclusions In this multicentre international cohort, patients with SSc and SBI implanted before disease onset showed higher rate of anti-RNAP3 positivity as compared to expected frequency and to matched controls. SBI were mainly implanted for cosmetic reasons and synchronous breast cancer had low frequency in both groups, highlighting that the association with anti-RNAP3 with SBI is independent from the one with breast cancer previously documented. Clinical features were similar to matched controls, except for lower prevalence of arrhythmias in cases.Abstract P.377 Table 1Continuous variables presented as median (1-3 IQR) (n available data) and compared with Mann-Whitney test; categorical variables as number/number available data (%) and compared with Fisher’s exact test