Recent studies have highlighted that somatic loss of function mutations in the tumour suppressor gene ARID1A underpin 57% of ovarian clear cell carcinomas (OCCC) 1, 2, 40% of uterine endometrioid carcinomas 3 and between 20 and 36% of uterine carcinosarcomas 4, 5, 6; however, they are rare in high‐grade serous ovarian carcinoma (HGSOC)1, 2. The gene discussed is ARID1A; the disease is ovarian clear cell cancer.