Retrospective Investigation of Case Studies to Determine the Concurrent Malignancy Rate Associated with Microscopic Polyangiitis

Introduction: This retrospective study investigated the concurrence rate and clinical characteristics of recently developed malignancies with microscopic polyangiitis (MPA). Materials and Methods: The subjects included 42 Japanese MPA cases (16 males and 26 females) that had been newly admitted to the hospital. Recent occurrences of malignancy (defined as malignancies diagnosed upon admission and up to two years prior to admission) and the presence of organ lesions were evaluated. As a control, recent occurrences of malignancy in 126 patients with rheumatoid arthritis (RA) were evaluated in a similar manner. Results: Recently developed malignancies occurred significantly more often in the MPA group (19.0%) than in the RA group (6.3%; odds ratio (OR), 3.47 [95% CI, 1.21–9.93]; Fisher’s exact test, p = 0.029). All MPA-asso‐ ciated malignancies were solid cancers, and none were from hematopoietic origin. With regard to characteriza‐ tion of organ lesions, MPA cases with malignancies exhibited peripheral neuropathy significantly more often (75% vs. 32.4%; OR, 6.27; 95% CI, 1.09–36.25; p = 0.045) and glomerulonephritis less often (37.5% vs. 82.4%; OR, 0.13; 95% CI, 0.02–0.69; p = 0.020) than MPA cases without malignancies. Skin lesions were ob‐ served in approximately 50% of cases, and there was no significant difference between MPA groups with and without malignancies (26.5%; OR, 2.78; 95% CI, 0.57–12.51; p value, 0.236). Conclusion: MPA coincided with malignancies at a higher ratio than did RA. Therefore, it is recommended that those admitted for MPA should be thoroughly screened for malignancies.