This is a randomized prospective multicenter study evaluating the efficacy against placebo of cyclophosphamide in combination with prednisone in the treatment of systemic sclerosis related interstitial lung disease. Patients will be allocated, after randomization into two groups receiving both corticosteroids: a group of patients receiving placebo of cyclophosphamide and a group of patients treated with cyclophosphamide. Cyclophosphamide will be administered IV at a dose of 0.7 g / m (maximum 1200 mg) every 4 weeks. In patients over 65 or if the creatinine clearance below 30 ml / min the dose should be reduced to 0.6 g / m². The duration of treatment with cyclophosphamide will be 12 months.