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Letter to the editor
Caution over use of ES2 as a model of ovarian clear cell carcinoma
  1. Angie L M Kwok,
  2. Oscar Gee-Wan Wong,
  3. Esther S Y Wong,
  4. Obe Ka-Lai Tsun,
  5. Ka-Kui Chan,
  6. Annie Nga-Yin Cheung
  1. Department of Pathology, The University of Hong Kong, Hong Kong Special Administrative Region, People's Republic of China
  1. Correspondence to Professor Annie Nga-Yin Cheung, Department of Pathology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong; anycheun{at}

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Dear Sir,

Clear cell carcinoma (CCC) of the ovary is a subtype of epithelial ovarian cancer (EOC) known for its relative resistance to standard platinum-based chemotherapy and poor prognosis. CCC account for up to 25% of ovarian carcinomas in Japan while make up only about 10% in North America. Analysis of archived pathology records on cases of ovarian cancer managed by Queen Mary Hospital, Hong Kong, from January 1993 to June 2012 revealed that CCC constituted 22.4% of EOC locally. Moreover, its yearly incidence showed a significant increase (unpublished results). Studies on ovarian CCC are therefore important and of regional significance.

Genetic and molecular biological studies of ovarian CCC often involve in vitro experiments using several widely recognised ovarian CCC cell lines including ES2, TOV-21G, OVISE, OVTOKO and OVMANA.1 However, we found that ES2, a widely used ovarian CCC cell line established in the late 1980s, displayed unusual features distinct from other ovarian CCC cell lines. Such observations led us to question its true histological identity.

Verification of hepatocyte nuclear factor 1β (HNF-1β) expression in our ovarian cancer cell lines has been carried out. HNF-1β is a transcription factor found to be considerably upregulated in almost all ovarian CCC through CpG island hypomethylation but not in other histological subtypes …

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  • ALMK and OG-WW contributed equally to this manuscript.

  • Acknowledgements We would like to thank Dr Hiroaki Itamochi for providing ovarian clear cell carcinoma cell lines OVMANA, OVISE and OVSAYO.

  • Contributors Acquisition, analysis and interpretation of data: ALMK, OG-WW, ESYW, OK-LT and K-KC. Drafting the work or revising it critically for important intellectual content: ALMK, OG-WW and AN-YC. Final approval of the version to be published: AN-YC.

  • Funding This study is supported by Health and Medical Research Fund, Food and Health Bureau, Hong Kong Government (ref: 01121526).

  • Competing interests None.

  • Provenance and peer review Not commissioned; externally peer reviewed.