Immunohistochemical study of alveolar and embryonal rhabdomyosarcoma

Paraffin-embedded sections of 11 alveolar and 12 embryonal rhabdomyosarcomas, 12 lymphomas, five neuroblastomas, five extraskeletal neoplasms resembling Ewing's sarcoma, and six epithelial tumors were tested for immunoreactivity against myosin, myoglobin, and isozymes BB and MM of creatine kinase with a peroxidase-antiperoxidase method. Of the 23 cases of rhabdomyosarcomas 17 were positive for at least three of the antigenic determinants. In contrast, the other investigated tumors were consistently negative for all markers, with the exception of breast and prostatic carcinomas. Our results establish that the presence of three or four of the above markers in a tumor is strongly suggestive of a rhabdomyosarcoma and helpful in the distinction of alveolar and embryonal rhabdomyosarcomas from lymphomas, neuroblastomas, and extraskeletal neoplasms resembling Ewing's sarcoma.     

Epithelial membrane antigen--a diagnostic discriminant in surgical pathology: immunohistochemical profile in epithelial, mesenchymal, and hematopoietic neoplasms using paraffin sections and monoclonal antibodies

Glycoproteins isolated from human milk fat globule membranes, designated epithelial membrane antigen (EMA), have been detected immunohistochemically in most nonneoplastic epithelia and are potentially a highly effective marker for establishing the epithelial nature of neoplastic cells. With commercially available monoclonal antibodies and an indirect immunoperoxidase technique, EMA localization was evaluated in paraffin-embedded tissues from a wide variety of neoplasms (320 specimens). Adenocarcinomas from various primary sites (breast, lung, colon, stomach, pancreas, gallbladder, prostate, endocrine glands, ovary, kidney, thyroid) were immunoreactive for EMA in 88 of 97 cases (91 per cent). Cytoplasmic and apical luminal membrane staining were the most common patterns of immunoreactivity, with peripheral membrane staining or other patterns also seen in some neoplasms. Squamous cell (13 of 13 cases) and transitional cell (12 of 12 cases) carcinomas, small cell anaplastic carcinomas (12 of 12 cases), and mesotheliomas (six of six cases) were also uniformly EMA-positive. Malignant lymphomas of the Hodgkin's (15 cases) and non-Hodgkin's types (74 cases), except for the true histiocytic lymphomas and occasional T-cell lymphomas, were nonreactive for EMA. Neoplastic and nonneoplastic plasma cells showed variable EMA positivity. Endocrine neoplasms (17 cases), including carcinoid tumors, medullary carcinoma of thyroid, adrenocortical carcinomas and pheochromocytomas, and germ cell tumors (eight cases, embryonal carcinoma and seminoma), and a wide variety of soft tissue tumors (27 cases) generally lacked immunoreactivity for EMA; the exceptions to this finding were synovial sarcomas and an epithelioid sarcoma. Malignant melanomas (eight cases) were typically nonreactive. Based on the observations in this large series of neoplasms, EMA is an excellent marker of epithelial differentiation, appears to be highly reliable for discriminating between poorly differentiated carcinomas and malignant lymphomas, and is especially helpful in characterizing small cell anaplastic carcinomas. Epithelial membrane antigen immunoreactivity is well preserved in paraffin sections of routinely processed tissues, facilitating application of this technique in diagnostic surgical pathology.     

Expression of chromogranin a protein and messenger RNA and tyrosine hydroxylase protein in paraffin-embedded sections of neuroendocrine neoplasms

Forty-three neuroendocrine neoplasms were analyzed by immunohistochemistry for tyrosine hydroxylase and chrornogranin A and by in situ hybridization (ISH) for chrornogranin A messenger RNA (mRNA) using formalin-fixed paraffin-embedded tissue sections. These included pheochromocytomas (7), medullary thyroid carcinomas (5), small-cell lung carcinomas (5), olfactory neuroblastomas (5), neuroblastomas (10), ganglioneuroblastomas (5), and ganglioneuromas (6). Tyrosine hydroxylase was detected in all groups of tumors except the small-cell lung carcinomas, whereas immunoreactivity for chromogranin A protein was detected in all groups. ISH analysis for chromogranin A mRNA agreed with the immunohistochemical findings. Beta-actin mRNA was present diffusely in tumor cells, confirming the preservation of another mRNA. There was no apparent relationship between protein or mRNA expression and the degree of differentiation in the 21 neuroblastic tumors. These results indicate that tyrosine hydroxylase may be another useful marker for neuroblastic tumors and that chromogranin A mRNA can be detected in routinely processed formalin-fixed paraffin-embedded tissue sections.     

Immunohistochemical analysis of Ewing''s sarcoma cell surface antigen p30/32MIC2.

Monoclonal antibody (MAb) HBA71, which was raised against Ewing's sarcoma cells, recognizes a cell-surface glycoprotein, p30/32MIC2, that is encoded by the MIC2 gene in the pseudoautosomal region of human chromosomes X and Y. This immunohistochemical study evaluates the specificity and sensitivity of MAb HBA71 for tumor diagnosis. Frozen and paraffin-embedded tissues of more than 300 tumors of diverse histologic type, including more than 100 small round cell tumors of childhood and adolescence, were tested with this MAb by the avidin-biotin immunoperoxidase procedure. The authors found HBA71 immunoreactivity in 61 of 63 Ewing's sarcomas studied and 9 of 11 primitive neuroectodermal tumors and peripheral neuroepitheliomas. HBA71-negative tumors included neuroblastomas (0 of 24), melanomas (0 of 13), an esthesioneuroblastoma, small cell osteosarcomas (0 of 2), a malignant ectomesenchymoma, desmoplastic SRCT (0 of 5), and medulloblastomas (0 of 5). Heterogeneous expression of HBA71 immunostaining was found in some embryonal rhabdomyosarcomas (3 of 14) and astrocytomas (4 of 7), and in a few neuroendocrine tumors (4 of 26), carcinomas (3 of 94), and lymphomas (6 of 30). Because Ewing's sarcomas are consistently HBA71 positive, the authors searched for antigen-positive normal cells that may represent precursors for these tumors; however, no obvious candidate for the elusive cell of origin for Ewing's sarcoma was identified in the normal fetal tissues tested. Their findings indicate that HBA71 is a highly restricted cell-surface antigen of Ewing's sarcomas and primitive neuroectodermal tumors, and immunohistochemistry employing this antibody may be of value in the differential diagnosis of selected small round cell tumors in childhood and adolescence.     

Immunohistochemical analysis of neural cell adhesion molecules. Differential expression in small round cell tumors of childhood and adolescence.

The neural cell adhesion molecule (NCAM) was discovered in a search for cell surface antigens of chicken neurons that contribute to cell adhesion and pattern formation during development. Homologous adhesion molecules have been identified in several species, including humans. In this immunohistochemical study, the authors examine the role of human NCAM in tumor diagnosis. The authors used a monoclonal antibody (MAb), 5.1H11, to examine NCAM immunoreactivity in frozen sections of more than 450 tumors, including more than 80 small round cell tumors (SRCT) of childhood and adolescence (neuroblastomas, Ewing's sarcomas [ES], peripheral neuroepitheliomas [PN], primitive neuroectodermal tumors [PNET], esthesioneuroblastomas, malignant ectomesenchymoma, medulloblastomas, small cell osteosarcomas, mesenchymal chondrosarcomas, embryonal rhabdomyosarcomas, and lymphomas). The authors show that 1) neuroblastomas and primary brain tumors are NCAM+; 2) ES, most PN/PNETs, and melanomas are NCAM-; 3) embryonal rhabdomyosarcomas and various other sarcomas are NCAM+; 4) neuroendocrine tumors are NCAM+; 5) subsets of carcinomas of kidney, ovary, lung and other organs are NCAM+; and 6) lymphoid tumors are NCAM-. Tests with normal fetal and adult tissues indicate that these findings reflect only in part the NCAM phenotypes of corresponding normal tissues. Notably the NCAM- phenotype of ES and PN/PNET is not explained by current histogenetic models for these tumors, which suggest a primitive neuroectodermal origin. Finally the authors show that NCAM expression among SRCT has an inverse relationship with the expression of p30/32MIC2, a cell surface antigen of ES and PN/PNET detected with MAb HBA71. These results suggest that immunohistochemical assays for NCAM and p30/32MIC2 expression may aid in the further characterization of SRCT of childhood and adolescence.     

Expression of HER-2/neu receptor protein in adrenal tumors

The HER-2/neu protein is overexpressed in many human carcinomas obtained from different tissues and may represent a useful target for therapy with the commercially available monoclonal antibody trastuzumab (herceptin). Novel therapeutic options are needed for metastasized adrenocortical cancer. Therefore, we studied expression of the HER-2/neu cell surface receptor protein using three different antibodies in 12 adrenal adenomas, 17 adrenocortical carcinomas and 5 pheochromocytomas. Normal adrenals (n = 5) served as controls. One adenoma showed very weak membranous immunostaining with the Dako antibody, two others showed a nonspecific cytoplasmic staining pattern. A nonspecific reaction in the cytoplasm was demonstrable in seven carcinomas with the Novocastra antibody. In all pheochromocytomas, a granular intracytoplasmic and, rarely, slightly membranous immunostaining with the Dako antibody was found. From our data we conclude that specific and significant membranous immunostaining indicating strong overexpression (grade 3) of HER-2/neu protein is not present in adrenocortical tumors. The granular cytoplasmic immunostaining of the medulla may be helpful for differentiation of adrenocortical tumors from pheochromocytomas.     

Antibody specific to muscle actins in the diagnosis and classification of soft tissue tumors

A series of soft tissue tumors, melanomas, carcinomas, and lymphomas were studied immunohistochemically for the presence of muscle actins (MA) with the monoclonal antibody HHF-35, and for the presence of desmin for comparison. In nonneoplastic tissues, MA immunoreactivity was present in skeletal and smooth muscle cells, in the pericytes of small vessels, and in the myoepithelial cells. Desmin immunoreactivity had a similar distribution, except that the pericytes of small vessels and myoepithelial cells were negative. All 17 rhabdomyosarcomas were positive for both MA and desmin. Of leiomyosarcomas, 31/32 were positive for MA, and 29/32 for desmin. In pleomorphic undifferentiated sarcomas (malignant fibrous histiocytomas) MA and desmin-positive cells were present in 9/35 and 5/35 cases, respectively. Three of five pleomorphic liposarcomas showed MA-positive tumor cells, which were also desmin-positive in one case. Desmoid tumors often showed a moderate number of both desmin- and MA-positive cells. Hemangiopericytoma, Kaposi's sarcoma, and endometrial stromal sarcoma showed MA-positive staining only in the pericytes and not in the neoplastic cells. In various types of carcinomas, melanomas, and lymphomas, MA- or desmin-positive neoplastic cells were not identified. MA, but not desmin, was present in the desmoplastic stroma in many carcinomas. Both MA and desmin are good markers for muscle differentiation and especially serve to identify rhabdomyosarcomas and leiomyosarcomas. These markers are also present in some sarcomas currently regarded as nonmuscle tumors. This may suggest that some of these tumors have differentiation properties related to true myosarcomas. The absence of muscle actin, a pericytic marker, in hemangiopericytoma does not confirm the concept of pericytic nature of this tumor.     

Small round blue cell tumours: diagnostic and prognostic usefulness of the expression of B7-H3 surface molecule

Aims:  To assess whether the expression of B7-H3 surface molecule could improve differential diagnosis of small cell round tumours.
Methods and results:  One hundred and one well-characterized paraffin-embedded small round cell tumours, stored in the pathology archive of the Gaslini Institute, were immunohistochemically analysed with the 5B14 monoclonal antibody, which recognizes the surface molecule B7-H3. All lymphoblastic lymphomas and the blastematous component of Wilms' tumours were completely negative and a few Ewing's sarcoma and Burkitt's lymphoma specimens showed focal positivity, whereas 74% of neuroblastomas, 67% of rhabdomyosarcomas and 100% of medulloblastomas were positive. The pattern of immunoreactivity of 5B14 mAb observed in rhabdomyosarcoma, neuroblastoma and medulloblastoma specimens was limited to the cytoplasmic membrane, and in neuroblastomas areas of rosette formation or of ganglion differentiation were preferentially stained. Interestingly, in neuroblastoma patients high expression of the antigen recognized by the 5B14 mAb was associated with a worse event-free survival.
Conclusions:  The 5B14 mAb represents an additional tool for the differential diagnosis of small round cell tumours and might be useful in identifying neuroblastoma patients at risk of relapse who may take advantage of more careful follow-up.     

Esthesioneuroblastoma. Intermediate filaments, neuroendocrine, and tissue-specific antigens

Esthesioneuroblastoma (EN), a malignant neuroblastic tumor arising in the superior portion of the nasal cavity, shares histologic similarities with a number of primary malignant tumors that arise in this region, including rhabdomyosarcoma, lymphoepithelioma, and lymphoma. To establish an antigenic profile of EN as an aid in the differential diagnosis of these histologically similar nasal tumors, immunostaining was performed for the following intermediate filaments: keratin, neurofilament, glial fibrillary acidic protein, and desmin; neuron-specific enolase (NSE), S-100 protein, chromogranin, human common leukocyte antigen (HLE), epithelial membrane antigen (EMA), myoglobin, and carcinoembryonic antigen (CEA) on 21 primary nasal tumors: eight EN, five lymphoepitheliomas, two small cell carcinomas, three lymphomas, and three rhabdomyosarcomas. Keratin and CEA stained only the carcinomas (6/7+, 4/7+), respectively; desmin and myoglobin only rhabdomyosarcoma (3/3+, 1/3+); and HLE only lymphomas (3/3+). Chromogranin and neurofilament staining occurred exclusively in one case each of EN. S-100 and NSE commonly stained EN (5/8+, 6/8+), but carcinomas (1/7+, 2/7+) and rhabdomyosarcomas (1/3+, 3/3+) were also positive. Despite the apparent nonspecificity of NSE and S-100, an antigenic profile of positive NSE of S-100 staining with negative epithelial, muscle, and lymphoid antigens uniquely identified six of eight EN. Chromogranin and neurofilament positivity was further evidence for EN in two cases. This antigenic profile is a helpful adjunct in the diagnosis of EN and other primary malignant nasal tumors.     

P63 in pulmonary epithelium,pulmonary squamous neoplasms,and other pulmonary tumors

p63 is a p53-homologous nuclear protein that appears to play a crucial role in regulation of stem cell commitment in squamous and other epithelia. In this study, p63 expression was examined in benign lung and in neoplasms of pulmonary origin. Eighty sections from routinely fixed and processed archival bronchoscopic biopsy or lobectomy specimens were pretreated with citric acid (pH 6.0) for antigen retrieval, then incubated overnight with anti-p63 monoclonal antibody 4A4. Slides were stained using a streptavidin-biotin kit and diaminobenzidine as chromagen, and were counterstained with hematoxylin. In normal lung, p63 intensely stained nuclei of bronchial reserve cells but did not stain ciliated cells, alveolar epithelial cells, or nonepithelial cells. The lower strata of squamous metaplastic bronchial epithelium stained positively. All squamous-cell carcinomas stained positively (n = 30). In some well-differentiated carcinomas, staining was found at the periphery of tumor nests but was negative in central zones showing squamous maturation. Poorly differentiated carcinomas showed very high proportions (80% to 100%) of p63-positive nuclei. All small-cell carcinomas were p63 negative (n = 9). Staining of bronchioloalveolar carcinomas (n = 7) and adenocarcinomas (n = 23) was variable: some tumors showed no detectable staining, others showed heterogeneously positive staining. Adenosquamous carcinomas (n = 5) displayed a unique basalar staining pattern. Carcinoid tumors were almost entirely negative (n = 5). We conclude that p63 is expressed in benign bronchial stem cells, in neoplastic cells with either squamous differentiation or squamous differentiating potential, and in a subpopulation of adenocarcinomas. p63 immunostaining may also aid in some histopathologic distinctions, such as in small biopsies where the differential diagnosis is poorly differentiated squamous carcinoma versus small-cell carcinoma. A stem cell biology-based classification system for squamous carcinomas is proposed.     

Myogenin is a specific marker for rhabdomyosarcoma: an immunohistochemical study in paraffin-embedded tissues.

Myogenin belongs to a group of myogenic regulatory proteins whose expression determines commitment and differentiation of primitive mesenchymal cells into skeletal muscle. The expression of myogenin has been demonstrated to be extremely specific for rhabdomyoblastic differentiation, which makes it a useful marker in the differential diagnosis of rhabdomyosarcomas (RMS) from other malignant small round cell tumors of childhood. Commercially available antibodies capable of detecting myogenin in routinely processed formalin-fixed paraffin-embedded (FFPE) tissue are now available. In this study, we evaluated myogenin expression using the monoclonal myf-4 antibody (Novocastra Labs) on FFPE in a large number of pediatric tumors in order to define the clinical utility of this marker. A total of 119 tumors were studied. These included 48 alveolar RMS (ARMS), 20 embryonal RMS (ERMS), one spindle cell RMS, 16 Ewing's sarcomas (ES), six nephroblastomas, two ectomesenchymomas, seven precursor hematopoietic neoplasms, five olfactory neuroblastomas, three neuroblastomas, six desmoplastic small round cell tumors, and five rhabdoid tumors. Distinct nuclear staining for myogenin was noted in all 69 RMS. Notably, the number of positive tumor cells differed between the ARMS and ERMS. In ARMS, the majority of tumor cells (75 to 100%) were positive, in contrast to ERMS, in which the positivity ranged from rare + to 25% in all but three tumors. Additionally, myogenin positivity was seen in two of two ectomesenchymomas and in two nephroblastomas with myogenous differentiation. All other tumors were clearly negative. Our results indicate that staining for myogenin is an extremely reliable and specific marker for rhabdomyoblastic differentiation. It gives consistent and easily interpretable results in routinely fixed tissues.     

Expression of myogenic regulatory proteins (myogenin and MyoD1) in small blue round cell tumors of childhood.

The distinction of rhabdomyosarcoma (RMS) from other small blue round cell tumors of childhood, such as Ewing's sarcoma/peripheral primitive neuroectodermal tumor (pPNET) and neuroblastoma, continues to present a diagnostic challenge to pathologists. The recent recognition of the master role of myogenic regulatory proteins in skeletal muscle commitment and differentiation, and the availability of monoclonal antibodies to two of them (myogenin and MyoD1), has prompted us to test their diagnostic utility in routinely processed, formalin-fixed, and deparaffinized tissue. Preliminary studies had demonstrated that, with the use of heat-induced epitope retrieval techniques, expression of myogenin and MyoD1 could be documented specifically in nuclei of fetal skeletal muscle by the respective antibodies. We performed a retrospective immunohistochemical analysis on 72 cases of small blue round cell tumors, including 33 RMSs, 1 metastatic myogenous Wilms' tumor, 26 Ewing's sarcomas/pPNETs, and 12 neuroblastomas. Nuclear expression of myogenin and MyoD1 were both found in 30/33 non-overlapping cases of RMS, with no significant differences in the sensitivity with respect to histological subtypes, and in 1/1 case of myogenous Wilms' tumor. None of the neuroblastomas or Ewing's sarcomas/pPNETs demonstrated positive nuclear staining with either antibody. However, most of the neuroblastomas, and occasional Ewing's sarcomas/pPNETs, showed variable fibrillary, cytoplasmic immunoreactivity with antibody to MyoD1. We conclude that, with the use of microwave-based epitope retrieval, antibodies to myogenin and MyoD1 are both useful markers for the identification of RMS among other small blue round cell tumors of childhood, but antibodies to myogenin have technical advantages over those to MyoD1, as the latter may cross-react with an unknown cytoplasmic antigen in non-muscle cells and tumors.     

Immunohistochemistry on needle biopsies of childhood malignancies.

Ultrasound-guided percutaneous needle biopsy proved to be a reliable and safe method to obtain material for histopathological and immunohistochemical diagnosis prior to treatment in childhood malignancies. A principal tumour identification could be obtained by a combined morphological and phenotypic examination of 38 small-sized tumour biopsy specimens using a fairly limited panel of immunological reagents, including antibodies to leucocyte common antigen (CD 45), certain B- and T-cell markers, various intermediate filaments (cytokeratin, desmin and vimentin), and neuroblastoma cells (UJ 167.11, A2B5, and UJ 13A; the latter recognizes NCAM). Five undifferentiated neuroblastomas were all positive with the neuroblastoma antibodies but negative for the other markers, including vimentin. The negative reactivity for desmin and vimentin was the major immunohistochemical distinction between neuroblastomas and rhabdomyosarcomas. In addition, limited reactivity with the neuroblastoma antibodies was seen in blastematous parts of Wilms' tumour, duct-like structures in a hepatoblastoma, and in tumour cells in a few undifferentiated myelo- and lympho-proliferative lesions. This study shows the importance of a combined evaluation of morphology and the pattern of immunoreactivity employing multiple markers.     

34betaE12 Cytokeratin Immunodetection in the Differential Diagnosis of Small Cell Tumors of Lung

The group of small cell tumors of the lung includes fine following: (1) small cell carcinoma (SCC) of neuroendocrine (NE) origin, (2) poorly differentiated squamous carcinoma, (3) the rare basaloid (basal cell) carcinomas, and (4) malignant lymphomas, primitive neuroectodermal tumors (PNETs), and rhabdomyosarcomas. The differential diagnosis among these entities carries a heavy therapeutic impact but may be difficult in small biopsy specimens or in cytologic material, especially if necrosis or artifactual alterations are present. The use of additional techniques such as immunostaining for NE markers is not always helpful, since immunoreactive chromogranin A is detectable in only a small percentage of small cell carcinomas. It has recently been reported that in the aerodigestive tract 34betaE12 cytokeratin (CK) immunostaining selectively labels non-NE carcinomas, including squamous cell carcinoma, adenocarcinoma, and the rare basaloid carcinoma. We evaluated the role of such CK immunodetection in the differential diagnosis of small cell lung tumors in cytologic and biopsy specimens. Eighty-one lung tumors diagnosed by means of endoscopic bronchial biopsy, fine needle aspirate, or bronchial washing were collected. They included 43 small cell NE carcinomas and 38 cases used as controls (comprehensive of 2 large cell neuroendocrine carcinomas, 4 carcinoid tumors, 30 cases of non-NE lung carcinomas, 2 cases of bronchial infiltration by non-Hodgkin lymphomas). 34betaE12 CK immunoreactivity was found in 29/30 cases of non-NE carcinomas, but in only 3/43 SCCs. The latter showed positivity in only a few scattered cells. The 2 cases of bronchial infiltration by malignant lymphoma as well as the 4 cases of carcinoid tumors and the 2 cases of large cell neuroendocrine carcinomas were negative. These findings were confirmed in the surgical specimens of operatedon cases. We conclude that, in lung carcinoma biopsies showing a small cell pattern, presence of 34betaE12 CK immunoreactivity favors a non-NE carcinoma, whereas its absence supports the diagnosis of SCC. Int J Surg Pathol 8(4):317-322, 2000     

Polyclonal anti-PSA is more sensitive but less specific than monoclonal anti-PSA: Implications for diagnostic prostatic pathology

Prostate-specific antigen (PSA) production by nonprostatic tissues has been reported, casting doubts on its specificity. The immunohistochemical relative specificity and sensitivity of PSA expression using monoclonal and polyclonal anti-PSA was analyzed on 60 prostate carcinomas, 40 normal seminal vesicles, and 310 nonprostatic tumors. All nonprostatic tumors proved negative with both antibodies. However, 13 (32%) seminal vesicles showed immunoreactivity with polyclonal anti-PSA, but none showed immunoreactivity with the monoclonal antibody. The sensitivity of the 2 antibodies for prostate cancer varied with tumor grade. In Gleason pattern 3, both antibodies showed diffuse immunostaining in all cases. In Gleason pattern 5, polyclonal anti-PSA showed diffuse (>95%) tumor cell positivity in 18 cases (90%), while with the monoclonal antibody, 7 cases (35%) showed only focal (<10%) tumor cell immunoreactivity. Thus, monoclonal anti-PSA seems to be useful in small gland proliferations in which the differential diagnosis includes seminal vesicle, while for poorly differentiated neoplasms, polyclonal anti-PSA is considered superior. Sections of high-grade prostate cancer should be included as positive controls for PSA immunostaining.     

The application of immunocytochemical techniques to routinely-fixed and stained cytologic specimens. An aid in the differential diagnosis of undifferentiated malignant neoplasms.

Routinely-fixed and Papanicolaou stained smears with the cytologic diagnosis of undifferentiated malignant neoplasm that had been prepared with cells obtained by fine needle aspiration biopsy (n = 7), pulmonary lavage (n = 5), or thoracentesis (n = 3) from 15 unselected patients were stained by an immunocytochemical technique to evaluate the presence of keratin proteins and the leukocyte common antigen (LCA). Commercially available, well-characterized monoclonal antibodies with specificities for keratin proteins and the leukocyte common antigen, and a streptavidin-biotin-horseradish peroxidase labelling method were used. Evaluation of the stained smears revealed the presence of one of the two antigens in material obtained from each patient, thus indicating the probable cell-lineage of the neoplastic cells. The specificity of the monoclonal antibody reagents used was further evaluated in routinely-fixed and stained cytologic material from 24 histologically confirmed carcinomas and 12 lymphomas. In conclusion, immunocytochemical techniques may be successfully applied to routinely processed archival cytologic smears to determine the antigenic profile of morphologically undifferentiated cells and therefore aid in the differential diagnosis of undifferentiated malignant neoplasms.     

Utilization of monoclonal antibody L26 in the identification and confirmation of B-cell lymphomas. A sensitive and specific marker applicable to formalin-and B5-fixed, paraffin-embedded tissues.

Immunophenotypic analysis of paraffin-embedded tissues of lymphoproliferative disorders has been facilitated by recent developments of monoclonal antibodies that react with epitopes that survive histologic processing. Leukocyte common antigen (LCA) antibody has made a significant contribution to the immunocytochemical separation of non-Hodgkin's lymphomas from nonlymphoid neoplasms. However, a small percentage of lymphomas, particularly some large cell or immunoblastic B-cell tumors, will not label with LCA antibody. Other antibodies, directed against B lymphocytes, experience problems of specificity and a lack of sensitivity when applied to formalin-fixed specimens. The authors recently investigated a monoclonal antibody (L26) that demonstrates excellent specificity and sensitivity for B lymphocytes, and tumors derived from them, in formalin- and B5-fixed, paraffin-embedded tissue. The avidin-biotin peroxidase complex (ABC) technique was utilized for immunostaining 95 cases of malignant lymphoproliferative disorders and a variety of normal and neoplastic nonlymphoid tissues. When applied to sections of benign lymphoid tissue, the L26 antibody labeled germinal center cells, mantle zone and scattered interfollicular lymphocytes, but not histiocytes or plasma cells. L26 marked 100% (44/44) of the large cell and immunoblastic B-cell lymphomas, along with 1 case of pre-B cell lymphoblastic lymphoma. This included 8 cases that were LCA-negative. None of the T-cell lymphomas or plasma cell tumors studied demonstrated L26 immunostaining. No normal, benign, or neoplastic nonlymphoid tissues examined stained with this antibody. L26 successfully labels B lymphocytes and B-cell lymphomas in routinely processed tissues, often with greater sensitivity and intensity than LCA. This antibody should prove invaluable in the investigation of atypical lymphoid proliferations and the identification of B-cell derived lymphomas, when fresh or frozen tissue is unavailable for analysis.