ACCME/Disclosures. Diagnosing Mesothelioma in Limited Tissue Samples. Papanicolaou Society of Cytopathology Companion Meeting March 12 th, 2016

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1 Diagnosing Mesothelioma in Limited Tissue Samples Papanicolaou Society of Cytopathology Companion Meeting March 12 th, 2016 Sanja Dacic, MD, PhD University of Pittsburgh ACCME/Disclosures GENERAL RULES FOR PATHOLOGIST WHEN DIAGNOSING Correlation with radiographic and intraoperative findings Dr. Sanja Dacic declares she has no conflicts of interest to disclose. A history of asbestos exposure should not be taken into consideration Adequate sample Perform appropriate immunohistochemistry 1

2 MORPHOLOGICAL CRITERIA FOR DIAGNOSIS OF MALIGNANT CELLULARITY/ZONATION MAJOR CRITERIA Zonation Cellularity Growth pattern Papillae Vascularity Stromal invasion MINOR CRITERIA Cytological atypia Mitoses Necrosis WHO 2015 Am J Surg Pathol 2000; 24(9): WHO 2015 ZONATION PLEURITIS STROMAL INVASION BENIGN PLEURA 2

3 How many pathologists are willing to diagnose mesothelioma in effusion cytology specimens? RESULTS OF MULTI-INSTITUTIONAL SURVEY 65% make a definitive diagnosis of MM in effusion material 94% of these stated that it is true for both primary and recurrence 63% stated that their clinicians would treat based on cytology diagnosis of MM Pintal A. et al. Cancer Cytopath 2013 DIAGNOSIS OF MM IN EFFUSION SAMPLES Mesothelioma Reactive mesothelial cells NO Inability to assess stromal invasion Minimal cytological atypia YES Architectural atypia large groups of mesothelial cells with knobby borders High cellularity Monotonous population of cells without easily identifiable benign mesothelial cells Pintal A. et al. Cancer Cytopath 2013 Courtesy of Dr. Sara Monaco, UPMC 3

4 SPECTRUM OF CHALLENGING CASES ROLE OF IMMUNOHISTOCHEMISTRY IN EFFUSION CYTOLOGY To support a diagnosis of MM vs. other malignancies To support a diagnosis of MM vs. reactive mesothelial cells Courtesy of Dr. Sara Monaco, UPMC VS. ADENOCARCINOMA IMMUNOHISTOCHEMISTRY OF EPITHELIOID VS. METASTATIC CARCINOMA MESOTHELIAL MARKERS SENSITIVITY/ SPECIFICITY Calretinin >90% CK5/ % WT % (~100%) D % ADENOCA MARKERS SENSITIVITY/ SPECIFICITY MOC31 >95% BerEP4 >95% BG8 (Lewis Y) >90% B % (>95%) TTF1 >80% (High) MARKER SENSITIVITY (%) SPECIFICITY VS. LUNG TTF-1 Napsin A BREAST ER PR GCDFP15 Mammaglobin KIDNEY PAX8 PAX2 RCC ~80 ~80 NA NA Up to 85 High High NA NA High High Unknown Unknown WHO

5 SARCOMATOID, DESMOPLASTIC AND BIPHASIC IMMUNOHISTOCHEMISTRY AND SARCOMATOID MARKER CYTOKERATIN (AE1/3,CAM5.2,CK7) CALRETININ DIAGNOSTIC USE Focal, weak, variable Usually focal in <10% of cells Sarcomatoid <10% Biphasic 10-15% D2-40 Usually helpful Other (WT-1, CK5/6, Ber-EP4, CEA, Not helpful MOC31) Desmoplastic <2% IMMUNOHISTOCHEMISTRY MESOTHELIAL HYPERPLASIA VS. Potential IHC markers in separation between benign and malignant mesothelial proliferations ANTIBODY HYPERPLASIA (%) (%) Desmin EMA p GLUT IMP BAP Attanoos RL. et al. Histopathology. 2003;43(3):231 8; Monaco S. et al. AJCP 2011; 135 (4):619 27; Shi M. et al. AJSP 2011; 33(6): 878; Bott M. et al. Nat Genet 2011; 43(7) : 668; Testa JR et al. Nat Genet 2011; 43(10):1022; Andrici J et al. Mod Pathol 2015(28):

6 BENIGN MESOTHELIAL CELLS VS. MM Desmin EMA p53 Diagnostic GLUT-1 Difficulties (glucose GLUT-1 transporter IHC 1) BENIGN MESOTHELIAL CELLS VS. MM Reactive 85% 20% 0% Reactive 3% 10% 80% 45% Malignant Malignant 67% % positive cases Attanoos RL. et al. Histopathology. 2003;43(3): Monaco et al. AJCP 2011; 135 (4): BAP1 (BRCA1-associated protein 1) IMMUNOHISTOCHEMISTRY IN MM Singhi A. et al. Mod Pathol 2016; 29:

7 IMMUNOHISTOCHEMISTRY MESOTHELIAL HYPERPLASIA VS. In the individual case, immunohistochemical staining reactions are simply too variable to be relied upon, and we do not recommend their use. Churg A, Cagle PT and Roggli VL. Tumors of the serosal membranes, AFIP Atlas of Tumor Pathology Series 4, pg. 100 (2006) While certain immunohistochemical stains are more likely to show positivity in benign proliferations and others in malignant proliferations, they should not be solely relied on for diagnosis in individual cases.. Husain A.et al. Guidelines for pathologic diagnosis of MM, 2013 Arch Pathol Lab Med A relatively large number of immunohistochemical markers for distinguishing between malignant mesothelioma and reactive mesothelial proliferations have been investigated, but the results of these studies remain controversial. No marker or combination of markers has yet been identified that can be used with confidence for routine diagnostic work in the differential diagnosis. WHO Nature Genetics 2016; Feb 29 on line GENETIC ALTERATIONS IN MALIGNANT 9p21 DELETION AND HISTOLOGY Loss of p16 (9p21) is the most common genetic alteration in MM Homozygous deletion, point mutation, methylation % Epithelioid Biphasic Sarcomatoid

8 DIAGNOSTIC UTILITY OF p16 DELETION APPROACH TO EFFUSION CYTOLOGY SAMPLES Fluid specimens Paraffin embedded tissue Modified from AJSP 2016, 40 (1) ATYPICAL MESOTHELIAL PROLIFERATION BAP1 IHC p16 BAP1- BAP1+ CEP9 p16 FISH Not deleted Deleted Not deleted Deleted Ilei et al. Cancer Cytopath 2003; 99(1): Chiosea et al. Mod Pathol 2008 Jun;21(6): Husain et al. Arch Pathol Lab Med ; 2012 Guidelines Deleted 29 DIAGNOSIS OF MM ESTABLISHED MM NOT EXCLUDED 2015 WHO classification of mesothelial tumors HISTOLOGICAL SUBTYPING OF EPITHELIOID Diffuse Malignant Mesothelioma Epithelioid Sarcomatoid Desmoplastic Biphasic Localized Malignant Mesothelioma Trabecular Tubulopapillary Micropapillary Epithelioid Sarcomatoid Biphasic Well-differentiated papillary mesothelioma Solid Pleomorphic 8

9 HISTOLOGICAL SUBTYPING OF EPITHELIOID ACCURACY OF SUBTYPING BIOPSY VS. RESECTION Kadota et al. JTO 2011 Chirieac et al. (submitted) SUMMARY Diagnosis of malignant mesothelioma in effusion and small biopsy specimens is possible and requires multidisciplinary approach Immunohistochemistry must be performed to confirm mesothelial origin Distinction between benign and malignant mesothelial proliferations remains a significant diagnostic problem Deletion of 9p21 (p16) as determined by FISH and BAP1 IHC may be diagnostically helpful 35 9