[1190] Well-Differentiated and Non-Invasive Diffuse Periteonal Mesotheliomas Treated with HIPEC: Histologic Spectrum

Michael Lee, Jennifer Collins, Allen Burke. UMMC, Baltimore, MD

Background: Well differentiated mesotheliomas include multicystic mesothelioma (MCM) and well-differentiated papillary mesothelioma (WDPM). Although many of these tumors are localized, some present with diffuse disease. Diffuse malignant mesothelioma of the epithelioid type may in some cases lack histologic evidence of invasion. We compared the histologic and clinical features of these three entities from a single institutional series of peritoneal mesothelioma.
Design: We retrospectively studied histologic specimens of 66 diffuse peritoneal mesotheliomas treated with hyperthermic intraperitoneal chemotherapy (HIPEC) after tumor debulking. Invasion was defined as absence of tumor within fat and tumor confined to surface projections on the serosa. MCM and WDPM were defined as previously reported.
Results: There were 15 well-differentiated and non-invasive mesotheliomas (23%): 3 WDPM, 4 MCM, and 8 non-invasive epithelioid mesotheliomas (NIEM). Five of 8 NIEM were in men, all 3 WDPM were in women, and 3 of 4 MCM were in women. The multicystic tumors occured in younger patients (32 ± 12 years) than the WDPM (55 ± 13 years) and NIEM (57 ± 11 years, p=.01). None of the patients with WDPM or MCM had prior surgery, compared to 5 of 8 NIEM. Two patients (one with WDPM and one with NIEM) had prior history of pneumonectomy for pleural mesothelioma. The mean peritoneal cancer index was identical in the WDPM and NIEM (16 ± 4), and slightly higher in MCM (23 ± 3, p = 0.3). Histologically, WDPM had surface non-invasive papillary projections lined by flattened cuboidal cells without nucleoli or pleomorphism; many papillae were vascular, and there were no or rare detached clusters. One WDPM had areas of infiltrating adenomatoid tumor, which was bland without mitotic activity or atypia. MCM was defined as possessing cysts lined by flattened epithelium without atypia, at least 2 mm in diameter, in a portion of the tumor. These tumors possessed a cellular stroma with stellate and spindled cells which was difficult to separate from invasion; one invaded into fat, with a prominent adenomatoid appearance. All of the multicystic tumors demonstrated persistence or recurrence (mean at 3 years), and one of the WDPM (15 years); none of the NIEM showed recurrence, but follow-up was short (mean 3.5 years).
Conclusions: Low-grade peritoneal mesotheliomas may have significant PCI and clinically mimic typical invasive malignant mesothelioma. These tumors can be be separated into three distinct histopathologic groups. In this small group with limited follow-up, MCM appears to be the most aggressive of the three.
Category: Gynecologic & Obstetrics

Wednesday, March 6, 2013 9:30 AM

Poster Session V # 185, Wednesday Morning


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