Bladder carcinoma associated with anti-NXP2-positive inflammatory myopathy: a case-based review

Anti-nuclear matrix protein 2 (NXP2) antibodies are increasingly recognized in adult idiopathic inflammatory myopathies (IIM) and have been associated with an elevated risk of malignancy. However, the spectrum of associated malignancies remains incompletely characterized. We report a case of anti-NXP2-positive myositis associated with bladder carcinoma in a 56-year-old man who presented with severe proximal muscle weakness, early dysphagia, and subcutaneous edema. Evaluation confirmed inflammatory myopathy, and myositis-specific antibody testing demonstrated anti-NXP2 positivity. Given the recognized association between anti-NXP2 antibodies and cancer-associated myositis, a malignancy workup identified urothelial carcinoma of the bladder. The patient received immunomodulatory therapy and transurethral resection of the bladder tumor. We performed a structured literature search in PubMed/MEDLINE, Scopus, Embase and reference-list screening from inception to May 2026. Search terms included combinations of "Myositis", "Dermatomyositis," "Polymyositis," "Autoantibodies," "Neoplasms", "Paraneoplastic Syndromes" and "Urinary Bladder neoplasms". Data extracted from eligible studies included patient demographics, inflammatory myopathy phenotype, anti-NXP2 antibody status, associated malignancies, and clinical characteristics. Forty-one relevant studies, including 20 observational cohorts or case series and 21 individual case reports, encompassing 411 patients were identified. Malignancy was reported in 63 patients, with the most common cancer types including prostate, lung, renal, thyroid, hematologic, gynecologic, and hepatocellular malignancies. To our knowledge, no previously published case of anti-NXP2-positive myositis associated with bladder carcinoma has been identified through our structured literature search. This case highlights a possible association and reinforces the importance of guideline-directed malignancy screening in adults with anti-NXP2 antibodies.