Reliability of PAX8 in clinical practice to accurately determine primary site of origin in female pelvic or abdominal lesions

Female patients with gynecological malignancies can harbor peritoneal pelvic or abdominal lesions; however, other primary tumors can involve the peritoneum as well. Since sampling of the peritoneum now can be easily performed by fine needle aspiration or percutaneous biopsy, we have noticed an increase in such procedures as initial attempts to establish a diagnosis. PAX8 has been used alone or in combination with other tumor markers to accurately classify these lesions and determine primary site of origin; however, prior published studies determined expression of PAX8 within historically diagnosed cases. We reviewed the reliability of PAX8 to determine tumor type or primary site in 135 current clinical pelvic or abdominal lesions and highlight several pitfalls in its routine use, in particular, relying on the presumed expression pattern (positive or negative) within a given primary tumor and that poorly differentiated endometrial endometrioid carcinomas or undifferentiated carcinomas may have patchy PAX8 expression or even lose expression within the primary tumor or the metastasis.