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BAF250a Expression in Atypical Endometriosis and Endometriosis-Associated Ovarian Cancer
  1. John P. Stamp, MD,
  2. C. Blake Gilks, MD,
  3. Martine Wesseling, MD,
  4. Sima Eshragh, MD,
  5. Kathy Ceballos, MD,
  6. Michael S. Anglesio, PhD,
  7. Janice S. Kwon, MD,
  8. Alicia Tone, PhD,
  9. David G. Huntsman, MD and
  10. Mark S. Carey, MD
  1. * Departments of Obstetrics and Gynecology, and
  2. Pathology and Laboratory Medicine, University of British Columbia, Vancouver, British Columbia, Canada;
  3. Faculty of Medicine, Universiteit van Amsterdam, Amsterdam, the Netherlands;
  4. § Department of Pathology and Laboratory Medicine, BC Cancer Agency;
  5. Genetic Pathology Evaluation Centre, University of British Columbia, Vancouver, British Columbia;
  6. Division of Gynecologic Oncology, Princess Margaret Cancer Centre, Toronto, Ontario; and
  7. # Hereditary Cancer Program, BC Cancer Agency, Vancouver, British Columbia, Canada.
  1. Address correspondence and reprint requests to Mark S. Carey, MD, Division of Gynecologic Oncology, University of British Columbia, 2775 Laurel St, 6th Floor, Diamond Health Centre, Vancouver, British Columbia, Canada, V5Z 1M9. E-mail: mark.carey{at}


Background and Objective Atypical endometriosis (AE) is thought to be a precursor lesion to the ovarian cancer subtypes associated with endometriosis, namely, endometrioid and clear cell carcinomas. ARID1A encodes a nuclear protein (BAF250a) governing chromatin remodeling, and mutations in ARID1A have been found in 30% to 50% of clear cell and endometrioid ovarian cancers. As BAF250a expression loss by immunohistochemistry (IHC) has been documented in the endometriosis precursor lesions closely associated with these ovarian cancers subtypes, our goal was to further study the association between BAF250a expression in cases of AE with and without an associated cancer.

Methods Three separate databases were screened for suspected cases of AE. Based on a detailed review of the pathology reports, we selected cases likely to contain AE for slide review. After slide review, tissue blocks were recalled to perform IHC for BAF250a in the associated cancer, AE, or typical endometriosis when present.

Results There were 35 cases of endometriosis-associated cancer and 8 cases of AE not associated with cancer. Atypical endometriosis was found on pathology review in 23 endometriosis-associated cancer cases (66%). In the 35 cancer cases, BAF250a IHC showed loss of expression in 14 cases. Atypical endometriosis was present in 10 of these cases, 6 of which showed BAF250a loss (60%). BAF250a loss was not observed in the 8 cases of AE not associated with cancer or in the contiguous AE of 13 cases, whereby BAF250a expression was retained in the associated cancer.

Conclusions BAF250a loss in AE is consistently associated with the development of BAF250a-negative endometriosis-associated cancers and appears to be an early event in most of these cases. This research provides additional evidence that in the absence of cancer, BAF250a expression should be evaluated as a biomarker of cancer risk in patients diagnosed with AE.

  • Endometriosis
  • Atypical endometriosis
  • BAF250a
  • ARID1A mutation
  • Endometriosis-associated ovarian cancer

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  • The authors declare no conflicts of interest.