Successful treatment of anti-melanoma differentiation-associated gene 5 antibody-positive dermatomyositis with rapidly progressive interstitial lung disease complicated by bilateral breast cancer following the additional tofacitinib: A case report.

Anti-melanoma differentiation-associated gene 5 (MDA-5) antibody-positive dermatomyositis (MDA5-DM) often causes rapidly progressive interstitial lung disease (RP-ILD). Although cancer complications in MDA5-DM are less frequently reported compared to other forms of DM, they do occur. For MDA5-DM patients with cancer, particularly in paraneoplastic settings, the primary treatment strategy often targets the malignancy first. However, surgery, chemotherapy, and radiotherapy carry significant risks of exacerbating ILD, especially in patients with respiratory failure. Despite improved prognosis with initial immunosuppressive combination therapy, some cases of MDA5-DM with RP-ILD remain refractory to treatment. Recent studies have shown the potential benefit of Janus kinase (JAK) inhibitors for refractory cases, though their impact on cancer progression remains a concern. We report a 48-year-old woman with MDA5-DM, RP-ILD, and bilateral breast cancer. Due to her respiratory condition, radical surgery and chemotherapy were initially not possible. Endocrine therapy and immunosuppressive therapy were administered, but the disease remained refractory. Tofacitinib, combined with plasma exchange, improved her ILD, allowing for bilateral mastectomy. One year later, MDA5 antibody titers became negative, and glucocorticoids were discontinued after two years. Three years later, neither MDA5-DM nor breast cancer has recurred. This is the first report of MDA5-DM complicated by breast cancer, and the first use of JAK inhibitors in such a case. Effective treatment requires close collaboration with oncologists to balance the risks and benefits of therapy in cases of MDA5-DM with RP-ILD and cancer.