Epithelial markers in prostatic, bladder, and colorectal cancer: an immunoperoxidase study of epithelial membrane antigen, carcinoembryonic antigen, and prostatic acid phosphatase

Use of Aleuria alantia Lectin Affinity Chromatography to Enrich Candidate Biomarkers from the Urine of Patients with Bladder Cancer

Developing a urine test to detect bladder tumours with high sensitivity and specificity is a key goal in bladder cancer research. We hypothesised that bladder cancer-specific glycoproteins might fulfill this role. Lectin-ELISAs were used to study the binding of 25 lectins to 10 bladder cell lines and serum and urine from bladder cancer patients and non-cancer controls. Selected lectins were then used to enrich glycoproteins from the urine of bladder cancer patients and control subjects for analysis by shotgun proteomics. None of the lectins showed a strong preference for bladder cancer cell lines over normal urothlelial cell lines or for urinary glycans from bladder cancer patients over those from non-cancer controls. However, several lectins showed a strong preference for bladder cell line glycans over serum glycans and are potentially useful for enriching glycoproteins originating from the urothelium in urine. Aleuria alantia lectin affinity chromatography and shotgun proteomics identified mucin-1 and golgi apparatus protein 1 as proteins warranting further investigation as urinary biomarkers for low-grade bladder cancer. Glycosylation changes in bladder cancer are not reliably detected by measuring lectin binding to unfractionated proteomes, but it is possible that more specific reagents and/or a focus on individual proteins may produce clinically useful biomarkers.

Mucin-producing tumors and tumor-like lesions involving the prostate: a comprehensive review

Mucin-producing tumors of the prostate include both primary and secondary tumors with mucinous differentiation or features involving the prostate gland. These tumors are relatively rare and have variable prognostic and therapeutic implications. Primary mucinous (colloid) adenocarcinoma of the prostate is defined as prostatic adenocarcinoma with mucinous differentiation involving 25% or more of the entire tumor. Another primary tumor of the prostate that may have mucinous features is primary mucin-producing urothelial-type adenocarcinoma of the prostate (mucinous prostatic urethral adenocarcinoma). Primary mucin-producing urothelial-type adenocarcinoma of the prostate is a distinct entity that typically arises from the prostatic urethra possibly from urethritis glandularis or glandular metaplasia with malignant transformation, and it is analogous to adenocarcinoma with mucinous differentiation arising from the urinary bladder. Signet ring cell tumors of the prostate, though rare, may also have mucinous features. Secondary tumors with mucinous differentiation that may involve the prostate include adenocarcinomas of the urinary bladder and colorectum. Pathologists should also be aware of mucin-producing tumor-like lesions involving the prostate, including mucinous metaplasia, and benign Cowper glands that may mimic malignancy. Herein we present an updated and comprehensive review of the clinicopathologic, immunohistochemical, molecular, and prognostic features of mucinous tumors and tumor-like lesions involving the prostate gland, with emphasis on mucinous prostatic adenocarcinoma and its mimickers, including potential diagnostic pitfalls.

Immunophenotype of high-grade prostatic adenocarcinoma and urothelial carcinoma

Morphologic features alone can usually be used to distinguish prostatic adenocarcinoma and urothelial carcinoma of the urinary bladder. Poorly differentiated tumors, however, can occasionally have features of both neoplasms, making determination of site of origin difficult. No study has provided a panel of antibodies to assist in the distinction of these two tumors. For this study, 73 examples of moderately and poorly differentiated prostatic adenocarcinoma and 46 examples of high-grade urothelial carcinoma were obtained from radical resection specimens. Immunohistochemical studies were performed using the following panel of antibodies: cytokeratin (CK) 7, CK 20, 34betaE12, Leu M1, carcinoembryonic antigen (CEA)m, CEAp, p53, Leu 7, prostate-specific acid phosphatase (PSAP), prostate-specific antigen (PSA), and B72.3. Mucicarmine was also performed. Intermediate and high-grade prostatic carcinoma were compared and then high-grade prostatic carcinoma was compared with high-grade urothelial carcinoma. PSA and PSAP each stained 94% of prostatic adenocarcinomas, but no urothelial carcinomas. Leu 7 stained 94% of prostate and 17% of urothelial carcinomas. Over half of the urothelial carcinomas showed positivity for 34betaE12 (65%), as did two cases of prostatic carcinoma (6%). Eighty-three percent of urothelial carcinomas and 12% of prostatic adenocarcinomas stained with CK 7. Forty-one percent of urothelial carcinomas and 12% of prostatic carcinomas were reactive for CEAm, and p53 stained 33% and 3% of urothelial and prostatic adenocarcinomas, respectively. No significant difference was seen in the expression of CEAp, CK 20, B72.3, Leu M1, or mucicarmine between prostate and urothelial carcinoma. We propose a panel of six antibodies to assist in the distinction of high-grade prostatic adenocarcinoma from high grade urothelial carcinoma: PSA, PSAP, 34betaE12, Leu 7, CK 7, and p53. The first three antibodies should be used initially; if results are negative, the remaining antibodies may be employed.

Mucinous adenocarcinoma of urinary bladder type arising from the prostatic urethra. Distinction from mucinous adenocarcinoma of the prostate

We describe two cases of mucinous adenocarcinomas involving and confined to the prostate and originating from the prostatic urethra. These cases were identical to adenocarcinomas arising within the urinary bladder and differed from mucinous adenocarcinoma of the prostate. In both cases, an in situ adenocarcinoma component was identified in the overlying prostatic urethra. In one case the in situ adenocarcinoma arose in a villous adenoma of the urethra. Both cases contained lakes of mucin lined by tall columnar epithelium with varying degrees of cytologic atypia, and one case had mucin-positive signet cells. In contrast, mucinous adenocarcinomas of the prostate demonstrate tubules and cribriform glands floating within mucin; mucin-positive signet cells are rare. Both tumors were negative immunohistochemically for prostate-specific antigen and prostate-specific acid phosphatase and positive for carcinoembryonic antigen. One case was treated by radical prostatectomy, and the patient was without evidence of disease with short follow-up. Following simple prostatectomy, the other patient did not undergo definitive therapy for several years, at which point the tumor had progressed locally to an advanced stage. In terms of therapy, the distinction between mucinous adenocarcinoma or urinary bladder-type arising in the prostate depicted within the current study and mucinous adenocarcinoma of the prostate is significant.

TDM35--a new monoclonal antibody to the XH1 cervical carcinoma cell line. Characterization and immunoperoxidase localization in benign and malignant tissues

The murine monoclonal IgG1 kappa antibody TDM35 was raised against the cervical carcinoma cell line XH1. The antibody recognizes 18.5-66 kDa NCA-like glycoproteins and immunostains a variety of formalin-fixed, paraffin-embedded normal, benign, and malignant tissues. It is of value in the diagnosis of carcinoma of the exocrine pancreas and it identifies foci of squamous and glandular differentiation in other tumours. TDM35 should form a useful addition to a panel of antibodies for the evaluation of epithelial lesions.

Extramammary Paget's disease and prostatic carcinoma

A patient with perianal extramammary Paget's disease (EMPD) occurring simultaneously with prostatic adenocarcinoma is presented. Four previously reported cases of genital EMPD associated with prostatic carcinoma are reviewed. The use of immunohistologic techniques to help establish the diagnosis in some cases, and the relationship of EMPD to underlying adenocarcinoma of sweat glands and of the lower urinary and gastrointestinal tracts is discussed. The importance of a directed search for internal malignancy in the individual patient with EMPD is emphasised.

Immunohistochemical and immunocytochemical study of bladder carcinomas using the epithelium-specific, tumour-associated monoclonal antibodies HMFG1 and AUA1

The antigenic expression of normal bladder epithelium and transitional carcinomas has been studied using the epithelium-specific, tumour-associated monoclonal antibodies HMFG1 and AUA1. Tissues from 79 cases of bladder carcinoma and 11 cases of non-neoplastic bladder tissues were stained with both the haematoxylin-eosin (H/E) and the indirect two-stage immunoperoxidase methods using the monoclonal antibodies (MAbs) HMFG1 and AUA1 at a concentration of 25 micrograms ml-1. Positive and negative controls were also used. Moreover, 46 urine smears prepared after cytocentrifugation were stained with both the Papanicolaou and the indirect two-stage immunoperoxidase methods. The results showed that HMFG1 reacted with the majority of cases of grade III carcinomas and carcinomas in situ and with a subset only of low-grade (I and II) carcinomas. The pattern of staining showed the following characteristics: (1) the epithelial surface membrane stained both in normal bladder and bladder carcinomas (surface of the papillae), (2) a variant number of cancer cells, increasing with the degree of malignancy, showed membrane and/or cytoplasmic staining, (3) tumours of the same histological grade showed antigenic heterogeneity. The MAb AUA1 was not widely expressed. The immunocytochemical study confirmed the reaction of HMFG1 with a variant number of malignant urothelial cells exfoliated in urine. Their reaction with AUA1 was much more limited. The immunocytochemical staining seemed to be more sensitive in the detection of malignant cells in some cases which had been characterized as negative or suspicious for malignancy by the Papanicolaou examination. The intravesical treatment with chemotherapeutic agents did not seem to influence the antigenic expression of malignant urothelial cells.

Primary transitional cell carcinoma of prostate: case with lymph node metastasis eradicated by neoadjuvant methotrexate, vinblastine, doxorubicin, and cisplatin (M-VAC) therapy

A case of transitional cell carcinoma of the periurethral prostatic ducts received neoadjuvant chemotherapy consisting of methotrexate, vinblastine, doxorubicin, and cisplatin (M-VAC), which eradicated pelvic lymph node metastasis, followed by cystoprostatectomy. M-VAC therapy may be indicated for metastatic transitional cell carcinoma of the periurethral prostatic ducts.

Epithelial markers in pancreatic carcinoma: immunoperoxidase localisation of DD9, CEA, EMA and CAM 5.2

Paraffin wax embedded, formalin fixed sections of 22 adenocarcinomas of the exocrine pancreas were stained with four mouse monoclonal antibodies: DD9-E7, an antibody raised against a human pancreatic tumour xenograft; carcino-embryonic antigen (CEA); epithelial membrane antigen (EMA); and cytokeratin (CAM 5.2). An indirect immunoperoxidase technique without enzyme pre-digestion and an affinity-purified sheep anti-mouse peroxidase conjugate were used. All of the tumours were positive for DD9-E7, EMA, and CAM 5.2. Twenty out of 22 were focally positive for CEA and the staining was often weak. As all of these adenocarcinomas were DD9-E7 positive, absence of staining for DD9-E7 in a tumour makes the diagnosis of adenocarcinoma of the exocrine pancreas very unlikely, and this is of value in distinction from endocrine carcinomas with a marked acinar pattern. The weak CEA staining distinguished pancreatic carcinomas from colorectal tumours. Because the distribution of staining for EMA and CAM 5.2 was no different from that previously seen in adenocarcinomas from other sites, these markers are likely to be of limited value in the differential diagnosis of abdominal adenocarcinomas of uncertain origin.

Detection of occult nodal metastases in patients with colorectal carcinoma

Immunohistochemical study may be used for detecting micrometastases by their expression of tumor-associated antigens. In 48 specimens of colorectal cancer from 47 patients, 49 of 249 lymph nodes (median, five per patient; range, 2-11) examined by light microscopic study contained tumor deposits. Sections of all lymph nodes were also examined by immunohistochemical study for carcinoembryonic antigen (CEA) and epithelial membrane antigen (EMA) expression using the indirect immunoperoxidase staining method. All 49 lymph node metastases (100%) from 20 patients stained positively for CEA and 45 (92%) expressed EMA. Of the 200 lymph nodes without metastases on light microscopic examination, anti-CEA revealed a single micrometastasis in a patient staged as Dukes' B. No additional metastases were detected with anti-EMA. In this series of patients immunohistochemical study has, therefore, influenced the histologic staging in only one patient (2%) and thus does not offer a significant benefit over conventional histologic staging.

A novel hybridoma antibody (PASE/4LJ) to human prostatic acid phosphatase suitable for immunohistochemistry

A murine monoclonal antibody PASE/4LJ to prostatic acid phosphatase (PAP) was used to immunostain a wide variety of sections of benign and malignant tissues (654 blocks). Non-neoplastic adult and fetal prostatic glands, primary and metastatic prostatic carcinomas, and scattered cells in prostatic and penile urethra were positive. Rat, dog and rabbit prostates were negative. Nine of 400 tumours of non-prostatic origin showed some positivity: 6/36 carcinoids, 1/9 islet cell tumours, 1/55 ovarian adenocarcinomas (serous) and one carcinosarcoma of the lung (epithelial portion). Positive staining was seen in islet cells in 4/5 specimens of normal pancreas, and in 4/9 blocks of normal pancreas surrounding a pancreatic tumour. Loops of Henle, maculae densae, and distal tubules in 10/10 fetal and 2/9 adult kidneys were also positive, with proximal tubules and collecting ducts negative. All other 159 blocks of non-neoplastic adult and fetal tissues were negative. The antibody was also affinity purified from ascitic fluid, and shown not to inhibit the enzyme activity of prostatic acid phosphatase.

Comparative study of carcinoembryonic antigen and epithelial membrane antigen expression in normal colon, adenomas and adenocarcinomas of the colon and rectum

The heterogeneous nature of tumour antigen expression may require selection of monoclonal antibodies on an individual patient or tumour basis to allow adequate tumour localisation. Carcinoembryonic antigen (CEA) and epithelial membrane antigen (EMA) expression has not previously been compared in colorectal cancer patients. Sections of cancer (n = 52), adjacent normal colon (n = 45), synchronous adenomas (n = 11) and nodal metastases (n = 49) were examined by indirect immunoperoxidase staining in 51 consecutive patients with colorectal cancer using monoclonal antibodies to CEA and EMA. The percentage of cells with positive staining in the primary tumours was graded 1: less than 25%, 2: 25-49%, 3: 50-75%, 4 greater than 75%. All primary colorectal cancers expressed CEA and 43 of 52 expressed EMA (83%). Grading showed CEA greater than EMA in 39, equal in 11 and less in two. Well differentiated cancers were more frequently graded three or four for CEA staining (23 of 27) than moderately differentiated cancers (11 of 22) (p less than 0.01). Equivalent figures for EMA were four of 27 and three of 22 (not significant) (NS) although the majority (86%) were graded 1 and 2. Grade 1 CEA expression was found in six of 15 proximal and only two of 37 distal lesions (p less than 0.01, chi 2 test) while for EMA equivalent figures were three of 15 and six of 37 (NS). Nodal deposits all expressed CEA and 45 of 49 expressed EMA (92%); 29 of 45 normal colon sections showed CEA expression (64%) as did all adenomas. EMA was not expressed by normal colon or adenomas. These results suggest that EMA expression is more specific but less sensitive than CEA for colonic cancer and is independent of tumour differentiation and site. Thus selecting monoclonal antibodies to CEA or EMA based on tumour biopsies may allow improved tumour localisation for imaging or therapy in patents with colorectal cancer.

Brenner tumor of the ovary: a correlative histologic, histochemical, immunohistochemical, and ultrastructural investigation

The histologic, histochemical, immunohistochemical, and ultrastructural features of Brenner tumor (BT) were studied. BT was compared with transitional bladder cells, and close similarities between the two tissues were identified. Abundant glycogen in all cellular layers, an alcianophilic/sialomucinic surface mucous coat, and argyrophilic cells characterized both BT and bladder epithelium. Immunohistochemically, chromogranin and neuron-specific enolase reactivity was observed in all cases examined. An additional relevant finding was the presence of serotonin-storing cells in both BT and urothelium. Moreover, carcinoembryonic antigen, epithelial membrane antigen, and keratin reaction were found in BT and urothelium, indicating an additional antigenic similarity. Additionally, malignant Brenner tumor was ultrastructurally found to share many common features with the bladder tissue. The distinct histochemical, ultrastructural, and antigenic pattern of BT, primarily of the transitional type, is emphasized.

HMFG-2 as a prognostic indicator in superficial bladder cancer

A series of transitional cell carcinomas and mucosal biopsy specimens of bladder were stained immunohistochemically with the monoclonal antibody HMFG-2. Staining characteristics ranged from luminal staining in well differentiated, superficial lesions to staining of all cells in invasive carcinomas. Invasive tumour nests also stained strongly with the antibody. There was good correlation between the staining pattern and histological assessment of both tumours and mucosal biopsy specimens. Correlation with clinical course showed that it was also a good predictor of subsequent disease progression of superficial tumours. It is suggested that HMFG-2 staining is a sensitive indictor of malignant transformation and that it may have a role as an adjunct to conventional histological examination in the assessment of urothelial carcinomas.

Detection of tumor cells in bone marrow of patients with prostatic carcinoma by immunocytochemical techniques

We used a mixture of antisera to prostatic specific acid phosphatase, prostatic specific antigen, epithelial membrane antigen and cytokeratin to examine multiple marrow aspirates from patients with local (15) and metastatic prostatic carcinoma (15), and benign prostatic hypertrophy (10). We found moderate to large numbers of tumor cells in the bone marrow of 11 of 15 (73 per cent) patients with known metastatic disease and small numbers of abnormal cells in 2 of 15 (13 per cent) patients with apparently local disease. No tumor cells were found in patients with benign prostatic hypertrophy, and only 2 patients with metastatic disease had tumor cells in the bone marrow when conventional hematomorphological preparations were examined. These findings suggest that immunocytochemistry can increase the detection rate of metastatic prostatic carcinoma cells. Further followup of larger numbers of patients with local carcinoma will reveal whether the presence of micrometastases denotes a poor prognosis.

A comparison of carcinoembryonic antigen (CEA) and epithelial membrane antigen (EMA) in human colorectal cancer

The development of monoclonal antibodies (MAbs) to tumour-associated antigens has allowed the successful radioimmunolocalization of a variety of tumours and has provided a basis for targeted therapy. In patients with colorectal cancer, antibodies to CEA have been the most widely used for imaging, but their role in targeted therapy may be inhibited by their reaction with normal tissues and with circulating CEA. Epithelial-membrane antigen (EMA) is expressed by most epithelial tumours, including colorectal cancers, and antibodies to EMA may provide a satisfactory alternative. We therefore compared two high-affinity MAbs, one to CEA (C46) and one to EMA (ICR2), in tissues obtained from 31 patients with cancer (18 primary colonic, 6 nodal metastases and 7 liver metastases), 14 patients with adenomatous polyps and 17 with normal colon. The indirect immunoperoxidase staining reaction was used and the results classified as either positive or negative. A heterogeneous pattern of staining was found for both antibodies. ICR2, the anti-EMA, reacted with slightly fewer colonic cancers than C46, the anti-CEA antibody (83% vs. 100%) and a similar number of metastases. Most noticeable was the minimal reaction of anti-EMA with normal colon (12% vs. 71%) and benign polyps (7% vs. 79%) in comparison to anti-CEA. This would suggest a possible role for ICR2 in the radioimmunolocalization and targeting of colorectal cancer.

Small cell carcinoma of the prostate. II. Immunohistochemical and electron microscopic studies of 18 cases

To evaluate the histogenesis of small cell carcinoma of the prostate, 18 cases of this tumor (9 pure small cell and 9 combined adeno- and small cell carcinoma) were studied using immunohistochemical methods. Seven of the small cell components also were assessed by electron microscopic examination. Using neuron-specific enolase (NSE), prostatic acid phosphatase (PAP), and prostate-specific antigen (PSA) on tissue sections, three distinctive immunostaining patterns of small cell carcinoma components were identified: staining positive for NSE and negative for PSA and PAP (10 cases), staining positive for PSA and PAP and negative for NSE (3 cases), and negative reaction for all three antigens (5 cases). Electron microscopic study demonstrated neurosecretory granules in two cases. Based on the immunostaining and electron microscopic findings, small cell carcinomas of the prostate appear to be a heterogeneous group of tumors. Some of them are neuroendocrine carcinomas whereas others are poorly differentiated adenocarcinomas or, possibly, reserve cell carcinomas. Differences in immunostaining patterns or presence and absence of adenocarcinoma component do not reflect any differences in the uniformly poor prognosis of small cell carcinomas, in which median survivals is 7.7 months. The authors believe that, because of such heterogeneity, small cell carcinomas of the prostate arise from multipotential prostatic epithelium and that an origin from specific neuroendocrine cells need not be implicated.

Cross reactivity of anti-epithelial membrane antigen monoclonal for reactive and neoplastic glial cells

An anti-epithelial membrane antigen monoclonal (Clone E29) was used as part of a panel of antisera in the investigation of primary CNS and metastatic tumours. In contrast to others, definite and often strongly positive cross-reactivity has been demonstrated on glial cells. The material consisted of fourteen astrocytomas, two ependymomas, six cerebral metastases and two cases of gliosis.

Ectopic prostatic glands in bulbar urethra. Immunoperoxidase study

Ectopic prostatic glands in the bulbar urethra of a sixty-year-old man were identified by an indirect immunoperoxidase stain for prostatic acid phosphatase. Cystoscopically the appearances were those of "urethritis" without the polypoid appearance previously reported in cases of ectopic prostatic tissue.

Carcinoembryonic antigen and beta-human chorionic gonadotropin as serum markers for advanced urothelial malignancies

Serum levels of carcinoembryonic antigen and beta-subunit of human chorionic gonadotropin were measured in 92 patients with advanced urothelial malignancies referred to us for chemotherapy. Elevations of carcinoembryonic antigen and/or beta-human chorionic gonadotropin occurred in 60 of the 92 patients (65 per cent). Minimal elevations (less than 50 per cent above the normal range) occurred in 25 patients (27 per cent), while 35 (38 per cent) had significant elevations (more than 50 per cent above the normal range). Of the latter patients carcinoembryonic antigen alone was elevated in 16 (17 per cent), beta-human chorionic gonadotropin alone in 13 (14 per cent) and both in 6 (6 per cent). Among the 24 patients with initially elevated levels whose markers were re-evaluated during therapy the marker levels correlated with disease course in all 15 whose elevations were more than 50 per cent and in 4 of 9 with minimal elevations. In patients with adenocarcinoma of the bladder the carcinoembryonic antigen level frequently was elevated (9 of 10). We conclude that serum levels of carcinoembryonic antigen or beta-human chorionic gonadotropin are significantly elevated (more than 50 per cent above the normal range) in 38 per cent of the patients with advanced urothelial malignancies and can be used as tumor markers, since they correlate with the clinical course of the patient and the response to therapy. Serum carcinoembryonic antigen levels usually are elevated in patients with bladder adenocarcinoma.

Origin of carcinomas causing bladder neck obstruction demonstrated by immunoperoxidase localisation of specific antigens

The immunohistological demonstration of prostate specific acid phosphatase, prostate specific antigen, epithelial membrane antigen and keratin was used to ascertain the origin of five advanced carcinomas involving the bladder neck and causing obstruction. Five prostatic carcinomas, 10 transitional cell and 10 squamous cell carcinomas with schistosomiasis of the bladder were studied for comparison. The concomitant localisation of prostate specific antigen and keratin was most useful in ascertaining the origin of tumour invading the bladder in contrast to the multiple use of other epithelial markers. It showed that 2/5 were of prostatic origin and 3/5 were urothelial. The markers did not discriminate with certainty between invasive poorly differentiated transitional or squamous cell carcinomas.

Evaluation of commercial immunoperoxidase kits for prostatic specific antigen and prostatic specific acid phosphatase

The practical application of commercially available immunoperoxidase kits for prostatic specific antigen (PSA) and prostatic specific acid phosphatase (PSPH) were blindly evaluated on routinely formalin fixed and paraffin embedded tissue from 95 consecutive cases of prostatic carcinoma, 10 cases of metastases from prostatic carcinoma and 90 cases of primary or metastatic non prostatic carcinoma. Both Kits showed a diagnostic specificity of 100%. The diagnostic sensitivities were 94% (PSA) and 90% (PSPH) respectively, but concomitantly staining for PSA and PSPH improved the diagnostic sensitivity to 99%. Using the histologic grading system of Gleason both markers showed a tendency to less extensive staining in low differentiated prostatic carcinomas. It is concluded that both Kits are highly specific and highly sensitive, but negative reaction in medium or low differentiated adenocarcinomas does not rule out the possibility of prostatic carcinoma.

A new monoclonal antibody to epithelial membrane antigen (EMA)-E29. A comparison of its immunocytochemical reactivity with polyclonal anti-EMA antibodies and with another monoclonal antibody, HMFG-2

Two polyclonal rabbit antibodies to epithelial membrane antigen (EMA), two mouse monoclonal antibodies (E29 and HMFG-2), and a "cocktail" of these two monoclonals have been compared using an indirect immunoperoxidase technique. Sections from 25 tissues (17 malignant and 8 benign), were examined. The distribution of staining with each of these reagents was similar, but the polyclonal antibodies produced stronger staining in colorectal carcinomas and lactating breast, whereas staining with the monoclonal antibodies was stronger in non-neoplastic pleural mesothelium and in pulmonary alveolar cells. When the two monoclonals were mixed there was no increase in staining intensity. E29 gave a "cleaner" result than HMFG-2, with better discrimination between cells and stroma, and is highly suitable for routine diagnostic histopathology.