Clinicopathological significance of loss of ARID1A immunoreactivity in ovarian clear cell carcinoma

Recent genome-wide analysis has demonstrated that somatic mutations in ARID1A (BAF250) are the most common molecular genetic changes in ovarian clear cell carcinoma (OCCC). ARID1A mutations, which occur in approximately half of OCCC cases, lead to deletion of the encoded protein and inactivation of the putative tumor suppressor. In this study, we determined the significance of loss of ARID1A immunoreactivity with respect to several clinicopathological features in a total of 149 OCCCs. First, we demonstrated that ARID1A immunohistochemistry showed concordance with the mutational status in 91% of cases with 100% sensitivity and 66% specificity. Specifically, among 12 OCCC cases for which ARIDA mutational status was known, ARIDIA immunoreactivity was undetectable in all 9 cases harboring ARID1A mutations and was undetectable in one of 3 cases with wild-type ARID1A. With respect to the entire cohort, ARID1A immunoreactivity was undetectable in 88 (59%) of 149 OCCCs. There was no significant difference between ARID1A negative and positive cases in terms of histopathologic features, age, clinical stage, or overall survival. In conclusion, this study provides further evidence that mutations in ARID1A resulted in loss of ARID1A protein expression in OCCC, although no significant differences between ARID1A positive and negative cases were observed with respect to any clinicopathological features examined.