Evaluating CA-125 and PET/CT for cancer detection in idiopathic inflammatory myopathies

OBJECTIVE: This study aims to evaluate the diagnostic accuracy of CA-125 and PET/CT in detecting cancer among adult patients with idiopathic inflammatory myopathy (IIM). METHODS: We conducted a retrospective study of a single-centre cohort of adult IIM patients enrolled from 2003 to 2020. Data on CA-125 and PET/CT tests conducted within five years of IIM symptom onset were extracted from electronic medical records. The outcomes assessed included true-positive, false-positive, true-negative and false-negative results. RESULTS: Among 1432 patients with IIM, 250 CA-125 tests were conducted on 205 patients within the first five years of symptom onset, yielding a false-positive rate of 3.1% and a false-negative rate of 14.3%. Most false-positives were associated with endometriosis or uterine fibroids, but additional medical procedures were often carried out to investigate the false-positive results. For PET/CT, 149 tests were performed on 139 patients, resulting in a false-positive rate of 5.5% and a false-negative rate of 28.6%. Lymphadenopathy and lung nodules were the predominant causes of false-positives, while melanoma, low-stage breast cancer and prostate cancer were the most frequent cancers missed (false-negatives). CONCLUSION: False-positive and false-negative results are prevalent in cancer antigen 125 (CA-125) and PET/CT testing for adult patients with newly diagnosed idiopathic inflammatory myopathy. Understanding the causes of these inaccuracies can aid clinicians in making informed decisions during patient care.