Differentiation of peritoneal mesothelioma and serous carcinoma

The differentiation of peritoneal epithelioid mesothelioma from serous papillary carcinoma of the ovary or peritoneum can be problematic. Most studies of the immunohistochemical differentiation of mesothelioma from adenocarcinoma have concentrated on pulmonary adenocarcinomas. However, several of the markers that are of proven utility in this context are less informative in the differentiation from serous carcinoma.

Papillary serous carcinoma

Peritoneal epithelioid mesothelioma

Calretinin

1/16¹, 4/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. <1% of cells; 1 case, 1-25% of cells; 3 cases)², 0/23 (Positivity required nuclear staining: 2 cases showed focal cytoplasmic staining)³, 5/13⁴, 8/26⁵, 14/45 (51-75% of cells: 3 cases [2 of these 3 cases were also strongly positive for BerEP4 but were negative for CK5/6; one was negative for MOC-31, the other showed trace positivity; electron microscopy was required to establish the diagnosis of serous carcinoma], 26-50% of cells: 3 cases, 1-25% of cells: 7 cases, <1% of cells: 1 case.)⁶

3/3¹, 35/35 (1-25% of cells; 3 cases, 26-50% of cells; 4 cases, 51-75% of cells; 11 cases, >75% of cells; 17 cases.)², 28/32 (staining was both nuclear and cytoplasmic)³, 40/40 (>75% of cells: 30 cases, 51-75% of cells: 9 cases, 26-50% of cells: 1 case. Staining was both cytoplasmic and nuclear.)⁶

The positivity of some serous carcinomas makes this marker less than specific.

CK5/6

11/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. <1% of cells; 5 cases ,1-25% of cells; 5 cases,26-50% of cells; 1 case)², 5/23³, 11/32⁷, 9/26⁵, 14/45 (26-50% of cells: 4 cases, 1-25% of cells: 7 cases, <1% of cells: 3 cases.)⁶

35/35 (26-50% of cells; 6 cases, 51-75% of cells; 8 cases, >75% of cells; 21 cases)², 17/32³, 37/40 (>75% of 10 cells: cases, 51-75% of cells: 12 cases, 26-50% of cells: 11 cases, 1-25% of cells: 3 cases, <1% of cells: 1 case. Staining was cytoplasmic.)⁶

This marker is of limited value in this context.

Thrombomodulin

7/20 (staining was focal, light and membranous)⁸, 1/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. <1% of cells in 1 case)², 6/23 (staining was focal)³, 2/45 (1-25% of cells: 1 case, <1% of cells: 1 case.)⁶

6/18 (staining was focal and membranous)⁸, 26/35 (1-25% of cells; 6 cases, 26-50% of cells; 9 cases, 51-75% of cells; 9 cases, >75% of cells; 2 cases.)², 18/32 (staining was focal and membranous)³, 29/40 (>75% of cells: 4 cases, 51-75% of cells: 7 cases, 26-50% of cells: 11 cases, 1-25% of cells: 6 cases, <1% of cells: 1 case. Staining was membranous)⁶

Results vary between studies.

D2-40

6/45 (26-50% of cells: 2 cases, 1-25% of cells: 4 cases. Staining was of the apical cell membrane)⁶, 98/169 (This was a study of cell blocks from serous effusions. 138 of these were serous carcinomas of ovary, primary of peritoneum (23 cases) or of Fallopian tube (8 cases). The paper does not state how many of the serous cases were positive. In 13 cases, 11-100% of the cells were positive, in 85 cases 10% or less of the cells were positive.)¹⁶

37/40 (>75% of cells: 17 cases, 51-75% of cells: 9 cases, 26-50% of cells: 7 cases, 1-25% of cells: 4 cases. Well differentiated tumours show staining of the apical cell membrane. Less well differentiated tumours show circumferential or discontinuous membrane staining.)⁶

The evidence from these two studies is conflicting..

Podoplanin

6/45 (26-50% of cells: 4 cases, 1-25% of cells: 2 cases. Staining was of the apical cell membrane.)⁶

37/40 (>75% of cells: 16 cases, 51-75% of cells: 8 cases, 26-50% of cells: 9 cases, 1-25% of cells: 4 cases. These were the same 37 cases that stained with D2-40 and the staining pattern was similar.)⁶

The specificity for mesothelioma is higher than that of calretinin but the sensitivity is lower.

BerEP4

25/30⁹, 45/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. 1-25% of cells; 4 cases, 26-50% of cells; 5 cases, 51-75% of cells; 14 cases, >75% of cells; 22 case)², 3/6¹⁰, 20/23³, 45/45 (>75% of cells: 34 cases, 51-75% of cells: 8 cases, 26-50% of cells: 2 cases, 1-25% of cells: 1 case. Staining was membranous)⁶

4/35 (<1% of cells; 1 case, 26-50% of cells; 3 cases.)², 3/32³, 5/40 (1-25% of cells: 3 cases, <1% of cells: 2 cases. Staining was membranous)⁶

Strong staining is a useful marker for serous carcinomas

B72.3

47/47¹¹, 33/46¹², 37/44¹³, 13/20¹⁴, 10/10¹⁵, 27/30⁹, 39/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. <1% of cells; 3 cases ,1-25% of cells; 12 cases, 26-50% of cells; 13 cases, 51-75% of cells; 8 cases, >75% of cells; 3 cases)², 33/45 (>75% of cells: 3 cases, 51-75% of cells: 4 cases, 26-50% of cells: 6 cases, 1-25% of cells: 13 cases, <1% of cells: 7 cases. Staining was apical membranous.)⁶

0/28¹², 3/10 (in 3 cases, less than 1% of cells were positive)¹⁴, 0/20¹⁵, 0/35², 0/40⁶

This marker has specificity for serous carcinomas but limited sensitivity.

CD15

34/46¹², 32/44¹³, 6/20¹⁴, 8/10¹⁵, 17/30⁹, 28/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. <1% of cells; 2 cases, 1-25% of cells; 9 cases, 26-50% of cells; 10 case, 51-75% of cells; 5 cases, >75% of cells; 2 cases)², 7/23³, 26/45 (51-75% of cells: 7 cases, 26-50% of cells: 10 cases, 1-25% of cells: 9 cases. Staining was membranous)⁶

3/28¹², 0/4¹⁴, 3/20¹⁵, 0/35², 2/32³, 0/40⁶

This marker has specificity for serous carcinomas but low sensitivity.

MOC-31

44/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. 1-25% of cells; 4 cases, 26-50% of cells; 16 cases, 51-75% of cells; 19 cases, >75% of cells; 5 cases)², 44/45 (>75% of cells: 29 cases, 51-75% of cells: 9 cases, 26-50% of cells: 4 cases, 1-25% of cells: 1 case, <1% of cells: 1 case. Staining was both cytoplasmic and membrane.)⁶

1/35 (1-25% of cells; 1 case.)², 2/40 (1-25% of cells: 1 case, <1% of cells: 1 case.)⁶

This marker may be very helpful in this context, with a higher specificity than Ber-EP4.

BG-8

33/45 (>75% of cells: 8 cases, 51-75% of cells: 6 cases, 26-50% of cells: 9 cases, 1-25% of cells: 8 cases, <1% of cells: 2 cases.)⁶

1/40 (<1% of cells: 1 case.)⁶

CD44H

5/23 (staining was membranous and seen in up to 50% of tumour cells)³

15/32 (staining was thick and membranous)³

No value

Ca19-9

31/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. < 1% 0f cells; 3 case, 1-25% of cells; 16 cases, 26-50% of cells; 9 cases, 51-75% of cells; 2 cases, >75% of cells; 1 case)²,

30/45 (51-75% of cells: 1 case, 26-50% of cells: 13 cases, 1-25% of cells: 15 cases, <1% of cells: 1 case.)⁶

0/35², 0/40⁶

This marker has specificity for serous carcinomas but low sensitivity.

Ca-125

42/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. < 1% of cells; case, 1-25% of cells; 17 cases, 26-50% of cells; 11 cases, 51-75% of cells; 13 cases, >75% of cells; 1 case)², 21/23 (staining was membranous)³

33/35 (1 case, 1-25% of cells; 12 cases, 26-50% of cells; 9 cases, 51-75% of cells; 8 cases, >75% of cells; 3 cases.), 8/32 (staining was membranous)³

Limited value

pCEA

7/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. <1% of cells; 3 cases ,1-25% of cells; 3 cases,51-75% of cells; 1 case)², 2/23³

3/32³

No value

mCEA

1/23³

0/32³

No value

HBME-1

40/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. 1-25% of cells; 4 cases, 26-50% of cells; 6 cases, 51-75% of cells; 11 cases, >75% of cells; 19 case)²

31/35 (1-25% of cells; 3 cases, 26-50% of cells; 5 cases, 51-75% of cells; 7 cases, >75% of cells; 16 cases.)²

No value

PLAP

11/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. < 1% 0f cells; 1 case, 1-25% of cells; 7 cases, 26-50% of cells; 3 cases)²

0/35²

No value

44-3A6

28/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. < 1% of cells; 3 cases, 1-25% of cells; 10 cases, 26-50% of cells; 9 cases, 51-75% of cells; 6 cases.)²

16/35 (<1% of cell; 1 case, 1-25% of cells; 7 cases, 26-50% of cells; 6 cases, 51-75% of cells; 2 cases.)²

No value

S-100

14/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. < 1% of cells; 3 case, 1-25% of cells; 7 cases, 26-50% of cells; 4 cases.)²

0/35²

No value

Vimentin

15/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. < 1% of cells; 4 cases, 1-25% of cells; 11 cases.)²

9/35 (<1% of cells; 1 case, 1-25% of cells; 8 cases.)²

No value

EMA

45/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. 1-25% of cells; 3 cases, 26-50% of cells; 9 cases, 51-75% of cells; 15 cases, >75% of cells; 18 cases.)²

35/35 (1-25% of cells; 3 cases, 26-50% of cells; 2 cases, 51-75% of cells; 7 cases, >75% of cells; 23 cases.)²

The optimum panel is probably BerEP4 and MOC-31 with calretinin, and either D2-40 or podoplanin^3,6.

Ultrastructure

Serous papillary carcinoma

Epithelioid mesothelioma

Microvilli

Straight microvilli of variable length, less prolific than in mesotheliomas and confined to the apical surface.Cell membranes are closely apposed. Intracytoplasmic lumina are absent.

Long slender branching microvilli. They may be confined to the apical surface, may also be present on the basal surface or may cover the entire cell membrane. Cells are separated by gaps that often contain microvilli. Microvilli may also be found on intracytoplasmic lumina.

Cytoplasm

Bundles of intermediate fibres are rare.

The cytoplasm contains numerous intermediate filaments arranged in bundles.

Ciliated cells

Multi-ciliated cells may occur

Rare

.

References

¹ Doglioni, C., Tos, A. P., Laurino, L., Iuzzolino, P., Chiarelli, C., Celio, M. R., Viale, G. Calretinin: a novel immunocytochemical marker for mesothelioma. Am J Surg Pathol1996;20:1037-46.

²Ordonez NG. Role of immunohistochemistry in distinguishing epithelial peritoneal mesotheliomas from peritoneal and ovarian serous carcinomas. Am J Surg Pathol 1998; 22:1203-14

³Attanoos RL, Webb R, Dojcinov SD, et al. Value of mesothelial and epithelial antibodies in distinguishing diffuse peritoneal mesothelioma in females from serous papillary carcinoma of the ovary and peritoneum. Histopathology 2002; 40:237-44

⁴Cathro HP,Stoler MH. The utility of calretinin, inhibin, and WT1 immunohistochemical staining in the differential diagnosis of ovarian tumors. Hum Pathol 2005; 36:195-201

⁵Chu AY, Litzky LA, Pasha TL, et al. Utility of D2-40, a novel mesothelial marker, in the diagnosis of malignant mesothelioma. Mod Pathol 2005; 18:105-10

⁶Ordonez NG. The diagnostic utility of immunohistochemistry and electron microscopy in distinguishing between peritoneal mesotheliomas and serous carcinomas: a comparative study. Mod Pathol 2006; 19:34-48

⁷Reis-Filho JS, Simpson PT, Martins A, et al. Distribution of p63, cytokeratins 5/6 and cytokeratin 14 in 51 normal and 400 neoplastic human tissue samples using TARP-4 multi-tumor tissue microarray. Virchows Arch 2003; 443:122-32

⁸Attanoos RL, Appleton MAC, Goddard H et al. Thronmbomodulin expression in malignant peritoneal mesothelioma and serous papillary adenocarcinoma of the ovary. J Pathol 1995;176:S49A.

⁹Rothacker D,Mobius G. Varieties of serous surface papillary carcinoma of the peritoneum in northern Germany: a thirty-year autopsy study. Int J Gynecol Pathol 1995; 14:310-8

¹⁰Cherchi PL, Marras V, Capobianco G, et al. Immunohistochemical evaluation of a new epithelial antigen, Ber-EP4, in ovarian cancer: preliminary results. Eur J Gynaecol Oncol 2001; 22:433-5

¹¹Thor A, Gorstein F, Ohuchi N, et al. Tumor-associated glycoprotein (TAG-72) in ovarian carcinomas defined by monoclonal antibody B72.3. J Natl Cancer Inst 1986; 76:995-1006

¹²Bollinger DJ, Wick MR, Dehner LP, et al. Peritoneal malignant mesothelioma versus serous papillary adenocarcinoma. A histochemical and immunohistochemical comparison. Am J Surg Pathol 1989; 13:659-70

¹³Wick MR, Mills SE, Dehner LP, et al. Serous papillary carcinomas arising from the peritoneum and ovaries. A clinicopathologic and immunohistochemical comparison. Int J Gynecol Pathol 1989; 8:179-88

¹⁴Khoury N, Raju U, Crissman JD, et al. A comparative immunohistochemical study of peritoneal and ovarian serous tumors, and mesotheliomas. Hum Pathol 1990; 21:811-9

¹⁵Wick MR, Mills SE,Swanson PE. Expression of "myelomonocytic" antigens in mesotheliomas and adenocarcinomas involving the serosal surfaces. Am J Clin Pathol 1990; 94:18-26

¹⁶Bassarova AV, Nesland JM,Davidson B. D2-40 is Not a Specific Marker for Cells of Mesothelial Origin in Serous Effusions. Am J Surg Pathol 2006; 30:878-82

This page last revised 24.7.2006.

	Papillary serous carcinoma	Peritoneal epithelioid mesothelioma
Calretinin	1/16¹, 4/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. <1% of cells; 1 case, 1-25% of cells; 3 cases)², 0/23 (Positivity required nuclear staining: 2 cases showed focal cytoplasmic staining)³, 5/13⁴, 8/26⁵, 14/45 (51-75% of cells: 3 cases [2 of these 3 cases were also strongly positive for BerEP4 but were negative for CK5/6; one was negative for MOC-31, the other showed trace positivity; electron microscopy was required to establish the diagnosis of serous carcinoma], 26-50% of cells: 3 cases, 1-25% of cells: 7 cases, <1% of cells: 1 case.)⁶	3/3¹, 35/35 (1-25% of cells; 3 cases, 26-50% of cells; 4 cases, 51-75% of cells; 11 cases, >75% of cells; 17 cases.)², 28/32 (staining was both nuclear and cytoplasmic)³, 40/40 (>75% of cells: 30 cases, 51-75% of cells: 9 cases, 26-50% of cells: 1 case. Staining was both cytoplasmic and nuclear.)⁶	The positivity of some serous carcinomas makes this marker less than specific.
CK5/6	11/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. <1% of cells; 5 cases ,1-25% of cells; 5 cases,26-50% of cells; 1 case)², 5/23³, 11/32⁷, 9/26⁵, 14/45 (26-50% of cells: 4 cases, 1-25% of cells: 7 cases, <1% of cells: 3 cases.)⁶	35/35 (26-50% of cells; 6 cases, 51-75% of cells; 8 cases, >75% of cells; 21 cases)², 17/32³, 37/40 (>75% of 10 cells: cases, 51-75% of cells: 12 cases, 26-50% of cells: 11 cases, 1-25% of cells: 3 cases, <1% of cells: 1 case. Staining was cytoplasmic.)⁶	This marker is of limited value in this context.
Thrombomodulin	7/20 (staining was focal, light and membranous)⁸, 1/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. <1% of cells in 1 case)², 6/23 (staining was focal)³, 2/45 (1-25% of cells: 1 case, <1% of cells: 1 case.)⁶	6/18 (staining was focal and membranous)⁸, 26/35 (1-25% of cells; 6 cases, 26-50% of cells; 9 cases, 51-75% of cells; 9 cases, >75% of cells; 2 cases.)², 18/32 (staining was focal and membranous)³, 29/40 (>75% of cells: 4 cases, 51-75% of cells: 7 cases, 26-50% of cells: 11 cases, 1-25% of cells: 6 cases, <1% of cells: 1 case. Staining was membranous)⁶	Results vary between studies.
D2-40	6/45 (26-50% of cells: 2 cases, 1-25% of cells: 4 cases. Staining was of the apical cell membrane)⁶, 98/169 (This was a study of cell blocks from serous effusions. 138 of these were serous carcinomas of ovary, primary of peritoneum (23 cases) or of Fallopian tube (8 cases). The paper does not state how many of the serous cases were positive. In 13 cases, 11-100% of the cells were positive, in 85 cases 10% or less of the cells were positive.)¹⁶	37/40 (>75% of cells: 17 cases, 51-75% of cells: 9 cases, 26-50% of cells: 7 cases, 1-25% of cells: 4 cases. Well differentiated tumours show staining of the apical cell membrane. Less well differentiated tumours show circumferential or discontinuous membrane staining.)⁶	The evidence from these two studies is conflicting..
Podoplanin	6/45 (26-50% of cells: 4 cases, 1-25% of cells: 2 cases. Staining was of the apical cell membrane.)⁶	37/40 (>75% of cells: 16 cases, 51-75% of cells: 8 cases, 26-50% of cells: 9 cases, 1-25% of cells: 4 cases. These were the same 37 cases that stained with D2-40 and the staining pattern was similar.)⁶	The specificity for mesothelioma is higher than that of calretinin but the sensitivity is lower.
BerEP4	25/30⁹, 45/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. 1-25% of cells; 4 cases, 26-50% of cells; 5 cases, 51-75% of cells; 14 cases, >75% of cells; 22 case)², 3/6¹⁰, 20/23³, 45/45 (>75% of cells: 34 cases, 51-75% of cells: 8 cases, 26-50% of cells: 2 cases, 1-25% of cells: 1 case. Staining was membranous)⁶	4/35 (<1% of cells; 1 case, 26-50% of cells; 3 cases.)², 3/32³, 5/40 (1-25% of cells: 3 cases, <1% of cells: 2 cases. Staining was membranous)⁶	Strong staining is a useful marker for serous carcinomas
B72.3	47/47¹¹, 33/46¹², 37/44¹³, 13/20¹⁴, 10/10¹⁵, 27/30⁹, 39/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. <1% of cells; 3 cases ,1-25% of cells; 12 cases, 26-50% of cells; 13 cases, 51-75% of cells; 8 cases, >75% of cells; 3 cases)², 33/45 (>75% of cells: 3 cases, 51-75% of cells: 4 cases, 26-50% of cells: 6 cases, 1-25% of cells: 13 cases, <1% of cells: 7 cases. Staining was apical membranous.)⁶	0/28¹², 3/10 (in 3 cases, less than 1% of cells were positive)¹⁴, 0/20¹⁵, 0/35², 0/40⁶	This marker has specificity for serous carcinomas but limited sensitivity.
CD15	34/46¹², 32/44¹³, 6/20¹⁴, 8/10¹⁵, 17/30⁹, 28/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. <1% of cells; 2 cases, 1-25% of cells; 9 cases, 26-50% of cells; 10 case, 51-75% of cells; 5 cases, >75% of cells; 2 cases)², 7/23³, 26/45 (51-75% of cells: 7 cases, 26-50% of cells: 10 cases, 1-25% of cells: 9 cases. Staining was membranous)⁶	3/28¹², 0/4¹⁴, 3/20¹⁵, 0/35², 2/32³, 0/40⁶	This marker has specificity for serous carcinomas but low sensitivity.
MOC-31	44/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. 1-25% of cells; 4 cases, 26-50% of cells; 16 cases, 51-75% of cells; 19 cases, >75% of cells; 5 cases)², 44/45 (>75% of cells: 29 cases, 51-75% of cells: 9 cases, 26-50% of cells: 4 cases, 1-25% of cells: 1 case, <1% of cells: 1 case. Staining was both cytoplasmic and membrane.)⁶	1/35 (1-25% of cells; 1 case.)², 2/40 (1-25% of cells: 1 case, <1% of cells: 1 case.)⁶	This marker may be very helpful in this context, with a higher specificity than Ber-EP4.
BG-8	33/45 (>75% of cells: 8 cases, 51-75% of cells: 6 cases, 26-50% of cells: 9 cases, 1-25% of cells: 8 cases, <1% of cells: 2 cases.)⁶	1/40 (<1% of cells: 1 case.)⁶
CD44H	5/23 (staining was membranous and seen in up to 50% of tumour cells)³	15/32 (staining was thick and membranous)³	No value
Ca19-9	31/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. < 1% 0f cells; 3 case, 1-25% of cells; 16 cases, 26-50% of cells; 9 cases, 51-75% of cells; 2 cases, >75% of cells; 1 case)², 30/45 (51-75% of cells: 1 case, 26-50% of cells: 13 cases, 1-25% of cells: 15 cases, <1% of cells: 1 case.)⁶	0/35², 0/40⁶	This marker has specificity for serous carcinomas but low sensitivity.
Ca-125	42/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. < 1% of cells; case, 1-25% of cells; 17 cases, 26-50% of cells; 11 cases, 51-75% of cells; 13 cases, >75% of cells; 1 case)², 21/23 (staining was membranous)³	33/35 (1 case, 1-25% of cells; 12 cases, 26-50% of cells; 9 cases, 51-75% of cells; 8 cases, >75% of cells; 3 cases.), 8/32 (staining was membranous)³	Limited value
pCEA	7/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. <1% of cells; 3 cases ,1-25% of cells; 3 cases,51-75% of cells; 1 case)², 2/23³	3/32³	No value
mCEA	1/23³	0/32³	No value
HBME-1	40/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. 1-25% of cells; 4 cases, 26-50% of cells; 6 cases, 51-75% of cells; 11 cases, >75% of cells; 19 case)²	31/35 (1-25% of cells; 3 cases, 26-50% of cells; 5 cases, 51-75% of cells; 7 cases, >75% of cells; 16 cases.)²	No value
PLAP	11/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. < 1% 0f cells; 1 case, 1-25% of cells; 7 cases, 26-50% of cells; 3 cases)²	0/35²	No value
44-3A6	28/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. < 1% of cells; 3 cases, 1-25% of cells; 10 cases, 26-50% of cells; 9 cases, 51-75% of cells; 6 cases.)²	16/35 (<1% of cell; 1 case, 1-25% of cells; 7 cases, 26-50% of cells; 6 cases, 51-75% of cells; 2 cases.)²	No value
S-100	14/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. < 1% of cells; 3 case, 1-25% of cells; 7 cases, 26-50% of cells; 4 cases.)²	0/35²	No value
Vimentin	15/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. < 1% of cells; 4 cases, 1-25% of cells; 11 cases.)²	9/35 (<1% of cells; 1 case, 1-25% of cells; 8 cases.)²	No value
EMA	45/45 (30 ovarian [10 primary and 20 metastatic to peritoneum] and 15 primary papillary serous carcinomas of peritoneum. 1-25% of cells; 3 cases, 26-50% of cells; 9 cases, 51-75% of cells; 15 cases, >75% of cells; 18 cases.)²	35/35 (1-25% of cells; 3 cases, 26-50% of cells; 2 cases, 51-75% of cells; 7 cases, >75% of cells; 23 cases.)²

	Serous papillary carcinoma	Epithelioid mesothelioma
Microvilli	Straight microvilli of variable length, less prolific than in mesotheliomas and confined to the apical surface.Cell membranes are closely apposed. Intracytoplasmic lumina are absent.	Long slender branching microvilli. They may be confined to the apical surface, may also be present on the basal surface or may cover the entire cell membrane. Cells are separated by gaps that often contain microvilli. Microvilli may also be found on intracytoplasmic lumina.
Cytoplasm	Bundles of intermediate fibres are rare.	The cytoplasm contains numerous intermediate filaments arranged in bundles.
Ciliated cells	Multi-ciliated cells may occur	Rare