[1080] The Utility of PAX8 in Patients with Both Breast and Mullerian Carcinomas

ED Euscher, MT Deavers. The University of Texas MD Anderson Cancer Center, Houston, TX

Background: The histologic and immunohistochemical features of breast and Mullerian carcinoma can overlap, and the distinction of metastatic carcinoma from a second primary may be problematic. PAX8, a transcription factor for organogenesis of the kidney, thyroid, and Mullerian system, has been described as a marker that distinguishes ovarian from breast carcinoma. In this study, tumors from patients with both breast carcinoma and Mullerian carcinoma (ovarian, peritoneal, or tubal) were stained with anti-PAX8 to determine its utility as a marker in a practical setting.
Design: Representative sections of the breast carcinoma and the Mullerian carcinoma from each patient were stained with anti-PAX8 (rabbit polyclonal, 1:100, Protein Tech Group, Inc Chicago, Il) using the BondMax autostainer. Staining was qualitatively assessed: negative, focal, or diffuse staining. Patient age at first cancer diagnosis, order of and interval between diagnoses of the breast and Mullerian carcinomas, and the histologic subtype of the tumors were recorded.
Results: Eight patients, 40 to 67 years old (mean 54 years) were identified. In 7 cases, the breast cancer diagnosis predated the Mullerian cancer by an interval of 2 to 10 years (mean 5.8 years). In one case, the patient presented with synchronous breast and ovarian carcinomas. Two patients had documented BRCA1 mutations, while BRCA status was unknown in 6 patients. In 3 of 7 patients treated at our institution, the primary Mullerian carcinoma had been misdiagnosed as metastatic breast carcinoma. In the eighth case, a consultation was sought for help in determining whether an ovarian tumor was metastatic breast carcinoma or a new primary. Six of the primary breast tumors were ductal carcinoma (5 invasive, 1 in-situ) and two were lobular carcinoma. All of the Mullerian carcinomas (5 ovarian, 2 peritoneal, 1 fallopian tube primary) were high grade serous carcinoma. All of the Mullerian carcinomas had moderate to strong diffuse staining for PAX8. None of the breast carcinomas had expression of PAX8.
Conclusions: The histologic distinction of metastatic breast carcinoma from primary Mullerian serous carcinoma remains problematic: nearly half of the cases in this series were initially misdiagnosed. The differential staining pattern of PAX8 in this series of patients with both serous carcinoma and breast carcinoma suggests that the marker can help distinguish a Mullerian primary from metastatic breast carcinoma. Consideration should be given to including this antibody in the evaluation of difficult cases.
Category: Gynecologic & Obstetrics

Wednesday, March 24, 2010 1:00 PM

Poster Session VI # 176, Wednesday Afternoon


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