[711] Histologic Subtypes and Pathologic Features of Epithelioid Malignant Peritoneal Mesotheliomas

Ashish P Mogal, Sanja Dacic, James Pingpank, David Bartlett, Alyssa M Krasinskas. University of Pittsburgh Medical Center, Pittsburgh, PA

Background: There is currently no grading or staging system for malignant peritoneal mesothelioma (MPM). Most MPM are characterized into epithelioid, biphasic and sarcomatoid types based primarily on pleural mesothelioma classification schemes. While the histologic subtype of many tumors critically impacts patient care and prognosis, only recently has an association been made between the histologic subtypes of epithelioid pleural mesotheliomas and clinicopathologic features. We sought to explore histopathologic variables of epithelioid MPM that may have clinical significance.
Design: 24 cases of chemotherapy-naive epithelioid MPM were reviewed. Mean patient age was 54.6 yrs with 5:1 male:female ratio. Histologic subtypes and pathologic parameters were recorded. To assess for CDKN2A/p16 deletions, FISH was performed using a CEP9 probe and a CDKN2A/p16 locus-specific probe.
Results: The following histological subtypes (predominant pattern) were observed: Papillary (no secondary subset), n=3, 12.5%; Tubular (pure tubules or acini), n=4, 17.5%; Tubulopapillary (varying combinations of tubules and papillae), n=8, 33%; Micropapillary (papillary tufts lacking a central fibrovascular core), n=1, 4%; Trabecular (arranged in thin cords), n=0, 0%; Solid (sheets/nests of polygonal to round tumor cells), n=8, 33%; and Pleomorphic (anaplastic or with prominent giant cells), n=0, 0%. The pathologic parameters included: Depth of invasion (superficial < 0.5 mm, n=6, vs. deep > 0.5 mm, n=18); Mitotic count (<5/50 HPF, n=17, vs. > 5/50 HPF, n=7); Nuclear grade (low, n=9, vs. high, n=15); Lymphovascular invasion (LVI), n=7; Lymph node metastasis (LNM), n=4/11; Stromal desmoplasia, n=15; and Lymphocyte host response (LHR), none-mild (n=17), moderate-severe (n=7). Interestingly, LNM was present in solid and tubulopapillary subtypes with deep invasion, low mitotic index, stromal desmoplasia, mild to severe LHR and no p16 deletion. By contrast, papillary subtype showed superficial invasion, no stromal desmoplasia, none to mild LHR, no LNM and p16 deletion in 2/3 cases.
Conclusions: Our preliminary analysis reveals that specific histologic subtypes of epithelioid MPM appear to correlate with clinicopathologic parameters. These histologic subtypes and pathologic features may help in the development of a staging and grading system for MPM. Study of additional cases and correlation with outcome will strengthen these observations and are currently underway.
Category: Gastrointestinal

Tuesday, March 20, 2012 9:30 AM

Poster Session III # 142, Tuesday Morning


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