Clinical associations of the AC-16 tropomyosin-like cytoplasmic ANA pattern with rheumatoid arthritis and malignancy in an ANA-tested population

Purpose: The aim of this study was to assess the clinical correlations of AC-16 tropomyosin-like cytoplasmic pattern positivity in a routine ANA-tested population. Meaterial and Methods: This retrospective case-control study had 310 patients, including 155 AC-16-positive individuals and 155 AC-16-negative controls. Demographic and clinical factors were analyzed across groups. Logistic regression analyses were conducted to determine both unadjusted and age- and sex-adjusted correlations between AC-16 positivity and specific clinical outcomes. A disease-matched subgroup analysis was also performed in patients with rheumatoid arthritis.Results: Patients positive for AC-16 demonstrated a higher prevalence of autoimmune diseases, rheumatoid arthritis, and malignancies in comparison to the control group. In unadjusted analyses, AC-16 positivity correlated with autoimmune disease (OR 1.64, 95% CI 1.03–2.62), rheumatoid arthritis (OR 2.53, 95% CI 1.13–5.67), and malignancy (OR 2.37, 95% CI 1.07–5.24). ROC analysis indicated modest discrimination for rheumatoid arthritis (AUC = 0.66) and any autoimmune disease (AUC = 0.63), while the discriminatory performance for malignancy was limited (AUC = 0.61). A subgroup analysis of rheumatoid arthritis patients revealed similar demographic and laboratory characteristics between the AC-16-positive and pattern-negative groups.Conclusion: AC-16 tropomyosin-like cytoplasmic pattern positivity is independently associated with autoimmune disease, particularly rheumatoid arthritis, as well as malignancy, whereas ANA-IIF titer levels do not appear to offer further clinical significance.