[329] Multiple Pathological Factors Contribute to Diagnostic Uncertainty in Mammary Low-Grade Adenosquamous Carcinoma. A Review of 35 Consultation Cases

GQ Young, SM Brandt, SA Hoda. Weill Cornell Medical College, New York, NY

Background: Low-Grade Adenosquamous Carcinoma (LGASC) is a rare but distinct form of mammary metaplastic tumor. In a retrospective review of LGASC cases seen in consultation, we observed that LGASC nearly always elicited diagnostic uncertainty among referring pathologists even on excisional biopsies. We sought to determine the basis for such uncertainty.
Design: All available histopathological material and archived records from LGASC cases (diagnosed on excisional biopsies, 1999-to date) in our consultation practice were reviewed.
Results: Thirty-five LGASCs were identified among 19,500 consultation cases (0.18%). 30/35 (86%) cases were submitted with an equivocal diagnosis (LGASC was mentioned in differential diagnosis in 3 cases) and 5 cases were submitted as 'positive' (all non-LGASC). All patients were female with unilateral (right: 22, left: 13) and unifocal disease. Mean age of patients was 62.4 (range 34-87) years and mean tumor size was 2.1 (range 0.6-5.0) cm. Based on correspondence, draft report or other communication, diagnostic uncertainty could be attributable to one or more of the following factors: (i) p63 positivity in tumor cell nuclei leading to erroneous interpretation of myoepithelial cells being present (i.e. non-invasive?); (ii) association with a dominant benign lesion including sclerosing papilloma in 14 (40%) cases, radial sclerosing lesion in 5 (14%), and adenomyepithelioma in 4 (11%); (iii) association with a high-grade spindle cell carcinoma in 6 (17%); (iv) location in nipple or subareolar tissue in 5 (14%), with secondary Paget's disease in 1 case; (v) triple-negativity: ER (-), PR (-) and Her-2/neu (-) in an otherwise low-grade tumor; (vi) association with in situ carcinoma in 5 (14%), including 3 LCIS. Seven (20%) cases recurred (mean time to recurrence: 40 months, range: 3-108) at the original site with histologically similar tumor (one adenomyoepithelioma with myoepithelial overgrowth recurred as LGASC in 22 mo). Lymph nodes were negative in all 15 cases for which lymph node information was available.
Conclusions: Multiple pathological factors contribute to diagnostic uncertainty in LGASC. These factors include misinterpretation of p63 immunostain, association with a dominant benign lesion or an in situ or a higher-grade carcinoma, subareolar or nipple location, and paradoxical triple-negativity in a low-grade tumor. Greater awareness of LGASC and its wide pathological spectrum could reduce diagnostic uncertainty in this tumor.
Category: Breast

Tuesday, March 10, 2009 1:00 PM

Poster Session IV # 23, Tuesday Afternoon