Microcarcinoma in the prostate: its association with duct-acinar dysplasia.

In a series of 100 prostatectomy specimens obtained for adenocarcinoma, 107 additional incidental microscopic (less than 0.05 cm3) carcinomas were identified. Their morphologic features including location, histologic grade, and associated premalignant changes were documented. In 51 cases there was strong evidence of transition between microcarcinoma and the premalignant lesion, duct-acinar dysplasia. Invasive cancer was usually related to dysplasia through a characteristic intermediate morphologic stage of transitive glands. These glands were smaller than prostatic ducts; they appeared to arise by budding from dysplastic duct walls and showed the same distinctive lining epithelium. They were distinguished from invasive glands by their pseudo-stratified epithelial lining and by consistent association with a sparse, discontinuous basal cell layer. Cytoplasmic differentiation at the point of junction of invasive cancer with transitive or dysplastic glands was studied by immunohistochemical staining for the differentiation markers prostate-specific antigen and pepsinogen II, and staining for mucin. Markedly reduced cytoplasmic differentiation was common in dysplastic and transitive glands. Invasion often coincided with an abrupt increase in cytoplasmic differentiation with expression of ectopic differentiation products. This sequence of biologic changes should be tested in other carcinomas where the exact point of invasion can be identified.     

Differentiation between metaplastic carcinomas and sarcomas of the human female breast by fibronectin

Summary The distribution pattern of fibronectin in metaplastic carcinomas, stromal sarcomas, malignant cystosarcoma phyllodes tumours and histiocytic type lymphomas of the human female breast has been studied using the indirect immunoperoxidase technique on formalin fixed paraffin embedded tissue.Fibronectin was demonstrated as intensely stained strands between tumour cells forming an irregular network in metaplastic carcinomas and lymphomas. Stromal sarcomas and the malignant stromal component of the phyllodes tumours exhibited, in contrast, a uniform staining throughout tumour cells and stroma which was weaker than in adjacent normal-looking connective tissue.We suggest that the intense staining reaction of metaplastic carcinomas is due to the scirrhous reaction generally associated with invasive human breast carcinomas. The advantage of using fibronectin as a diagnostic tool in the differentiation of carcinoma/lymphoma versus sarcoma is the fact that the antigen is a stromal marker and its staining intensity is not influenced by the morphology or degree of differentiation of non-mesenchymal tumours.     

The L1 antigen and squamous metaplasia in the bladder

The L1 antigen was investigated as a marker of squamous differentiation in urothelium using a monoclonal antibody Mac387, and the results were compared with the expression of high molecular weight cytokeratins. L1 antigen was consistently demonstrated in all instances of partial and complete squamous metaplasia and in squamous carcinomas. In contrast, pure transitional cell carcinomas (except one with minor focal staining), adenocarcinomas and normal and hyperplastic urothelium did not label. In a few squamous carcinomas in situ, the pattern of labelling obtained with Mac387 was different from that seen in invasive squamous carcinomas and metaplasias. Compared with high molecular weight cytokeratins, the expression of L1 was more intense in areas of squamous differentiation. L1 expression, as identified by antibody Mac387, may therefore serve as a useful marker of squamous differentiation in urothelial lesions.     

Immunohistochemical localization of S100 protein in skin tumors

We applied a peroxidase-antiperoxidase technique for S100 protein to 73 tumors of skin and skin adnexa. These included 15 eccrine tumors, 11 apocrine tumors, 18 tumors with differentiation toward hair, two sebaceous adenomas, one mixed tumor of the scalp, ten dermatofibromas, ten basal cell carcinomas, five squamous cell carcinomas, and one clear cell acanthoma. Consistent results were obtained. Occasional cells in eccrine tumors showed strong positive staining, as did the Langerhans' cells in the squamous cell carcinomas and the clear cell acanthoma. The cells of the apocrine tumors showed moderate to weak staining, and the tumors with differentiation toward hair, the sebaceous adenomas, and the mixed tumor of the scalp showed uniform negative staining, as did basal cell carcinomas and dermatofibromas.     

CD44 expression is a feature of prostatic small cell carcinoma and distinguishes it from its mimickers

Small cell neuroendocrine carcinoma of the prostate is a rare variant of prostatic cancer that shares morphologic similarity with prostatic adenocarcinoma of Gleason 5 pattern. It has also been considered morphologically and immunohistochemically indistinguishable from small cell neuroendocrine carcinomas of other origins. CD44 is a cell-surface molecule proposed to identify cancer stem/progenitor cells in prostate cancer. We performed immunohistochemical study for CD44 expression in 11 cases of prostatic small cell neuroendocrine carcinoma and compared its patterns of expression with 73 cases of prostatic adenocarcinoma and 47 cases of small cell neuroendocrine carcinomas of other organs. Strong and diffuse membrane staining for CD44 was observed in 100% of the prostatic small cell neuroendocrine carcinomas. In conventional adenocarcinomas of the prostate, positive staining was only seen in rare, scattered tumor cells; and CD44 staining was negative in most of the small cell neuroendocrine carcinomas of nonprostate origin. The difference in CD44 expression between small cell neuroendocrine carcinomas of the prostate and those of other organs are statistically significant (P < .001). Our study demonstrates the utility of immunohistochemical staining for CD44 in distinguishing prostatic small cell neuroendocrine carcinoma from its mimickers including prostatic adenocarcinoma of Gleason 5 pattern and small cell neuroendocrine carcinomas of other organs. CD44 is the first marker that shows a high degree of tissue/organ specificity for small cell neuroendocrine carcinomas. Because CD44 is a putative marker of prostate cancer stem cells, the strong and diffuse expression of CD44 and the lack of expression of prostate luminal differentiation markers androgen receptor and prostatic specific antigen in prostatic small cell neuroendocrine carcinomas suggest that the tumor cells may retain cancer stem cell features.     

Hep par 1 antibody stain for the differential diagnosis of hepatocellular carcinoma: 676 tumors tested using tissue microarrays and conventional tissue sections.

A well-characterized positive marker for hepatocellular differentiation would be a useful tool for the diagnosis of hepatocellular carcinoma (HCC). The recently commercially available Hep Par 1 antibody (clone OCH1E5.2.10) has been reported to be a sensitive marker for HCC in paraffin embedded sections. Of non-hepatocellular tumors, occasional carcinomas have been reported to stain, most frequently gastric adenocarcinomas. This study further evaluated the staining of this antibody on a large number of neoplasms using tissue microarray technology as well as conventional tissue sections. Six hundred seventy-six tumors, including 19 cases of HCC, were tested. Eighteen of 19 cases of HCC were positive, 3 showing <5% staining. Two cases negative on the array showed focal staining when whole tissue sections from the same tumors were used. 16 of 34 cases of gastric carcinomas gave positive reactions, 4 of these showed less than 5% staining. Staining of gastric carcinomas was not limited to signet ring-type carcinomas or to areas of hepatoid differentiation. Only 1 of 11 cases of cholangiocarcinoma showed focal staining. We also noted several other tumors to stain occasionally, including adrenal cortical carcinoma (3/13), yolk sac tumor (2/9), colonic adenocarcinoma (8/106), lung carcinoma (3/52), ovarian carcinoma (5/48), and endocervical adenocarcinoma (1/5). We did not observe staining in pancreatic carcinoma (11), renal cell carcinoma (36), breast carcinoma (85), melanoma (25), or mesothelioma (5). This study supports Hep Par 1 as a useful marker in the differential diagnosis of HCC, but with significant limitations. Cautious use of this antibody in a panel with other positive (alpha fetoprotein, CD10, polyclonal carcinoembryonic antigen) and negative (epithelial membrane antigen, monoclonal carcinoembryonic antigen, CD15) markers of hepatocellular differentiation may aid in the accurate diagnosis of HCC.     

Expression of the antigen detected by the monoclonal antibody Ca 19.9 in human breast tissues

Summary The incidence and significance of the expression of the antigen defined by the monoclonal antibody Ca 19.9 (Sialyl Le^a) has been assessed in human breast tissue. Frozen and formalin-fixed, paraffin embedded specimens of normal, hyperplastic, pregnant breast and carcinomas were examined using an immunoperoxidase technique.Ductal and acinar epithelium of normal and hyperplastic tissues showed variable reactivity in frozen sections but there was a reduction in staining in comparable samples after fixation and processing, such that in many instances only focal ductal epithelium reacted. A distinctive feature in the pregnant breast was the absence of staining in acini showing differentiated secretory activity, despite a reaction in adjacent non-secretory acini and ducts.The overall incidence of detection of the Ca 19.9 antigen in breast carcinomas was 62%, but in half of these only a small number of cells stained. A significant relationship between expression of Sialyl Le^a and poor differentiation of carcinomas was identified, but there was no correlation with local lymph node status. In contrast to the non-malignant tissue fixation and processing had little effect on the reactivity of carcinomas. It is suggested that this difference may be quantitative in nature, with malignant breast showing much greater expression, or be related to organisation of the antigen.The observations concerning carcinomas and pregnant breast indicate that the synthesis of the Ca 19.9 antigen is related to the state of differentiation and functional activity of human breast.     

Utility of 123C3 monoclonal antibody against CD56 (NCAM) for the diagnosis of small cell carcinomas on paraffin sections

CD56 is immunohistochemically detectable in virtually all small cell carcinomas on frozen sections. The authors retrospectively tested the usefulness of the monoclonal antibody 123C3 against CD56 to differentiate pulmonary and extrapulmonary small cell carcinomas from nonneuroendocrine non—small cell carcinomas by paraffin-section immunohistochemistry after antigen retrieval. The study included 70 small cell carcinomas and 344 primary and metastatic nonneuroendocrine carcinomas of various primary sites. The staining results were compared with specific neuroendocrine markers (CD57, Chromogranin A, Synaptophysin). The monoclonal antibody 123C3 diffusely stained most small cell carcinomas with a strong membranous pattern (sensitivity: 0.99). The staining intensity was not diminished in areas with crush artifacts or after decalcification. The neuroendocrine markers had a combined sensitivity of only 0. 44 for small cell carcinomas. With regard to nonneuroendocrine carcinomas, the 123C3 antibody stained 7 of 28 ovarian carcinomas, 6 of 30 renal cell carcinomas, 2 of 10 endometrial carcinomas, two of three nonneuroendocrine large cell carcinomas of the lung, 1 of 38 adenocarcinomas, and 4 of 52 squamous cell carcinomas of the lung. Urothelial carcinomas, hepatocellular carcinomas, squamous carcinomas of the head/neck and cervix uteri, as well as adenocarcinomas of the breast, stomach, colon, pancreas, and prostate, showed no immunoreactivity for CD56. The specificities of 123C3 and the combined neuroendocrine markers for small cell carcinomas were 0. 94 and 0. 95, respectively. The authors conclude that monoclonal antibody 123C3 might be useful for the immunohistochemical differentiation of small cell carcinomas from nonneuroendocrine carcinomas on paraffin sections, especially in small and crushed biopsy specimens.     

Distribution of the Ca (Oxford) antigen in lung neoplasms and non-neoplastic lung tissues.

The Ca (Oxford) antigen was originally isolated from a malignant neoplasm and with few exceptions was reported to discriminate between malignant and non-malignant neoplasms or normal tissues. Using the Ca 1 antibody we have studied the Ca distribution in 54 lung neoplasms and adjacent non-neoplastic lung tissue. Staining of tumours was very focal and the proportion of positive cells varied from about 50% for adenocarcinomas to less than 1% for oat cell carcinomas, which were often negative. Focal cytoplasmic staining can be seen in all neoplasms, whereas membrane staining is mainly seen in their areas of glandular and squamous differentiation. We found consistently strong membrane staining of alveolar type II pneumocytes in non-neoplastic lung. This staining may be useful in differentiating type II cells from alveolar macrophages which only occasionally showed granular cytoplasmic staining, probably due to phagocytosed Ca. Mucin from tumours and bronchi did not stain but there was consistent staining of alveolar serous exudate suggesting extracellular location of Ca.     

Epithelial markers in primary skin cancer: an immunoperoxidase study of the distribution of epithelial membrane antigen (EMA) and carcinoembryonic antigen (CEA) in 65 primary skin carcinomas

Sixty-five primary malignant skin tumours have been stained for carcinoembryonic antigen (CEA) and epithelial membrane antigen (EMA) using rabbit polyclonal affinity-purified antibodies and an indirect immunoperoxidase technique. The tumours consisted of 15 invasive squamous carcinomas, 23 basal cell carcinomas, 16 malignant eccrine poromas (porocarcinomas), and 11 sebaceous carcinomas. The basal cell carcinomas were negative for CEA and EMA except where there was keratotic or sebaceous differentiation. All the sebaceous and squamous carcinomas and 15/16 porocarcinomas contained EMA. 12/15 squamous carcinomas were positive for CEA. The malignant poromas were negative for CEA except on the ulcerated surface of two. In tumours classified as sebaceous carcinomas there was positive staining for CEA in some cells, cyst contents and/or keratotic foci. These findings have implications for the use of immunoperoxidase localization of epithelial markers in the differential diagnosis of primary and metastatic skin cancer.     

CA125 and thyroglobulin staining in papillary carcinomas of thyroid and ovarian origin is not completely specific for site of origin

AIMS: A 70-year-old woman presented with metastatic psammoma body-rich papillary carcinoma in a supraclavicular lymph node. No primary site was evident. The tumour showed strong staining for CA125 and weak staining for thyroglobulin. Prompted by this case we aimed to assess the reliability of immunostaining for CA125 and thyroglobulin in making the distinction between thyroid and ovarian papillary carcinoma. METHODS AND RESULTS: Nine papillary carcinomas of the thyroid and 17 serous papillary carcinomas of the ovary were stained for CA125 and thyroglobulin, as well as CAM 5.2, LP 34, carcinoembryonic antigen (CEA), S100 and diastase/periodic acid-Schiff. Nine of nine thyroid carcinomas stained for thyroglobulin; in addition CA125 was positive in four of nine. Normal surrounding thyroid also showed some reaction. Seventeen of 17 ovarian serous carcinomas were positive for CA125; in addition one case showed moderately strong staining for thyroglobulin. Mucin stains were positive in 14/17 ovarian serous carcinomas, but negative in all thyroid carcinomas. The other antibodies assessed showed no useful differences in staining frequency. Conclusion: Many cases of papillary carcinoma of the thyroid show CA125 staining, and this feature therefore has little positive predictive value for an ovarian origin. Occasional cases of ovarian papillary carcinoma may show staining for thyroglobulin, and this result should therefore be interpreted cautiously.     

Immunohistochemical analysis of thyroglobulin and keratin in benign and malignant thyroid tumours

Summary 56 thyroid gland tumours and non neoplastic alterations were studied for keratin and thyroglobulin staining, using the indirect immunoperoxidase method on serial formalin fixed paraffin embedded sections. Papillary carcinomas showed a strong reaction with anti-keratin serum but a weak reaction with anti-thyroglobulin serum. Follicular adenomas and carcinomas showed virtually no reaction for keratin but a strong reaction for thyroglobulin. Undifferentiated and medullary carcinomas did not react with either antiserum, except for single cells in two undifferentiated carcinomas which reacted with anti-keratin serum. In nodular goiters, hyperplastic follicles showed little or no reaction with anti-keratin serum and strong reaction with anti-thyroglobulin serum.It is suggested that this virtually type-specific staining for keratin or thyroglobulin may be related to different degrees of cellular differentiation and organelle content in the tumour cells.This work was supported by a grant from the Wilhelm-Sander-Stiftung (82.007.1)     

Relation between stage, grade, proliferation, and expression of p53 and CD44 in adenomas and carcinomas of the colorectum.

AIMS--To investigate the changes in and relations among p53, CD44 and MIB-1 expression in adenocarcinomas of the colorectum and to determine whether these changes are progressive across the adenoma-carcinoma sequence. METHODS--Expression of p53 protein, CD44 adhesion molecule and MIB-1 proliferation antigen was detected using immunohistochemistry in 68 colorectal carcinomas and 32 colorectal adenoma. The staining characteristics were compared with degree of dysplasia in adenomas, and differentiation and Dukes' stage in carcinomas. Results were analysed and assessed using Spearman's rank correlation and independent t tests. RESULTS--p53 staining was present in som adenomas and correlated with the degree of dysplasia. There was significantly more staining in carcinomas than adenomas and significant correlation between staining and Dukes' stage. CD44 staining was maximal in adenomas, diminished in carcinomas and was minimal in metastasising carcinomas. There was inverse correlation between p53 and CD44 expression across the adenoma-carcinoma-metastasising carcinoma sequence. MIB-1 expression was highest in carcinomas but did not correlate with either p53 or CD44 expression. CONCLUSIONS--There are progressive changes in p53, CD44 and MIB-1 expression in adenomas and carcinomas. A combination of these tests may prove useful in assessing which patients with adenomas are at greatest risk of progressing to carcinoma.     

Carcinoembryonic antigen and milk-fat globule protein staining of malignant mesothelioma and adenocarcinoma of the lung

Immunohistologic markers have been of considerable value in differentiating malignant mesothelioma from adenocarcinoma. Recently, staining for milk-fat globule (MFG) protein has been suggested as a useful diagnostic test for this separation, but subsequent reports have been conflicting, with some authors finding clearcut differences, while others showed similar marking of both tumor types. To examine this technique further, we studied lung carcinomas and mesotheliomas with commercially available anti-MFG, and compared these results with those obtained with anticarcinoembryonic antigen (CEA), a commonly used immunomarker of carcinoma. We found that carcinomas showed strong cytoplasmic staining for MFG and CEA; however, a greater percentage of carcinomas were more strongly positive for CEA than for MFG. Mesotheliomas did not, for the most part, stain strongly with either antibody. In addition, carcinomas from different hospitals stained differently for MFG, but not for CEA. We conclude that although strong cytoplasmic staining for MFG is a reasonably reliable indicator of carcinoma, CEA staining provides a better separation and is considerably easier to interpret in lung cancer specimens.     

Immunolocalization of urokinase-type plasminogen activator in adenomas and carcinomas of the colorectum

Carcinogenesis in the human colon is associated with a marked increase in the tissue content of the urokinase-type plasminogen activator (u-PA). This study was performed to determine the type of cells responsible for the u-PA increase in carcinomas of the colon and in their precursor lesions, the adenomas, by immunohistological evaluation applying monoclonal antibody 3689 directed to the beta-chain of u-PA. Normal intestinal mucosa (n = 17) showed hardly any staining of u-PA, but some lamina propria cells were faintly positive. Carcinomas (n = 17) and adenomas (n = 16) showed a considerable and comparable staining intensity of u-PA in neoplastic columnar epithelial cells, and this staining was found to be diffuse and cytoplasmic. In a majority of the neoplastic tissues the u-PA staining was found to be patchy and not related to known risk markers of malignancy such as dysplasia in the adenomas, or to prognostic determinants such as Dukes' classification or differentiation in the carcinomas. The observation of strong u-PA positive lamina propria cells in adenomas but infrequently observed in normal mucosa and carcinomas was noteworthy. u-PA staining intensity of the tissue sections was found to correlate well with the u-PA antigen level in the tissue extracts determined by ELISA (r = 0.52, P = 0.0001) but poorly with the u-PA activity determined enzymatically (r = 0.28, P = 0.05). In conclusion, the u-PA increase in neoplasia of the human colon can be attributed to an increased diffuse cytoplasmic content of u-PA in neoplastic columnar epithelial cells.     

Distribution of Leu-7 antigen (HNK-1) in thyroid tumors: its usefulness as a diagnostic marker for follicular and papillary carcinomas.

The reactivity of the anti-Leu-7 monoclonal antibody was tested in 39 neoplastic and nonneoplastic thyroid tissue specimens. These included eight colloid goiters, 14 follicular adenomas, nine papillary carcinomas, five follicular carcinomas, two medullary carcinomas, and one metastatic follicular carcinoma in bone. We observed strong cytoplasmic and/or cell membrane positivity in all follicular and papillary carcinomas, in both primary and metastatic tumors. However, the medullary thyroid carcinomas tested were negative. We also observed weak and only occasional staining with anti-Leu-7 antibody in colloid goiter and follicular adenomas. The staining in the benign thyroid lesions was usually focal, less than 10% of the cells; however, in cases of follicular and papillary carcinomas, both in primary and metastatic tumors, the staining was diffuse and strong. Some of the colloid material in colloid goiters and follicular adenomas showed faint homogenous staining with anti-Leu-7 antibody. Our findings suggest that anti-Leu-7 monoclonal antibody is a marker that may facilitate the differentiation between benign and malignant thyroid lesions, with the exception of medullary carcinoma. In addition, caution should be taken when using this antibody to diagnose metastatic lesions, as other metastatic carcinomas have also been reported to be positive. This antibody should be used in conjunction with a panel of antisera to complement a morphologic diagnosis.     

Expression of Tn and sialyl-Tn antigens in tumor tissues of the ovary.

The expression of sialyl-Tn and Tn antigens in various benign, borderline, and malignant ovarian tumors was examined immunohistochemically using newly developed antibodies specific for sialyl-Tn and Tn antigens. Sialyl-Tn antigen was detected in only one benign tumor, a mucinous adenoma that showed faint cytoplasmic staining in a few cells. However, sialyl-Tn was present in 5 of 12 serous borderline tumors, 10 of 19 mucinous borderline tumors, 10 of 13 serous adenocarcinomas, 15 of 16 mucinous adenocarcinomas, 14 of 15 endometrioid adenocarcinomas, and 7 of 7 clear cell carcinomas of the ovary. The antigen expression was observed throughout the cytoplasm of cancer cells and in the apical cytoplasm and luminal contents of some glands. The incidence and intensity of staining for sialyl-Tn antigen were higher in malignant tumors than in borderline tumors, but these results did not correlate with the histologic classification or differentiation. Coexpression of sialyl-Tn antigen and Tn antigen was observed in two serous adenocarcinomas, six mucinous borderline tumors, five mucinous adenocarcinomas, eight endometrioid, and seven clear cell carcinomas. In no case was Tn antigen expressed without concomitant sialyl-Tn antigen expression. Accumulation of sialyl-Tn antigen seems to be an early event of carcinogenesis of the ovary.     

In vivo demonstration of cytoplasmic fibronectin in human breast carcinomas

Summary The distribution pattern of fibronectin in 24 invasive human breast carcinomas has been studied using the indirect immunoperoxidase technique. A positive cytoplasmic staining reaction was observed in 16 tumours. Well-differentiated carcinomas showed weak or no staining, whereas all moderately or poorly differentiated carcinomas and one signet ring cell carcinoma contained fibronectin positive tumour cells with moderate or strong staining. The staining intensity was positively correlated to degree of anaplasia with the exception of two moderately differentiated duct carcinomas and the two medullary carcinomas, which were only slightly positive. Non-attached independently growing tumour cells stained more intensely than tumour cells in clusters. Pericellular fibronectin was found in only one carcinoma of medullary type. In normal ducts and glands it was seen at the stromal-epithelial junction corresponding to the basement membrane, around myoepithelial cells and along the luminal border. The results support the findings of several in vitro investigations that breast tumour cells synthesize fibronectin. It also suggests that cytoplasmic fibronectin expression might be an indicator of tissue differentiation in non-solidly growing invasive duct carcinomas of the human mammary gland.     

The significance of alpha-fetoprotein and other tumour markers in differential immunocytochemistry of primary liver tumours

One hundred benign and malignant primary liver tumours were screened immunocytochemically for alpha-fetoprotein (AFP), alpha 1-antitrypsin, alpha-human chorionic gonadotropin, carcinoembryonic antigen (CEA), keratin and vimentin. Alpha-fetoprotein was found in 16/63 (24%) hepatocellular carcinomas and in two hepatoblastomas. When comparing tissue positivity for AFP with tumour differentiation, grade 1 hepatocellular carcinomas were found to be negative, while 21% of grade 2, 36% of grade 3 and 16% of grade 4, respectively, stained positively. Alpha-fetoprotein positive cells were present in 9/10 hepatocellular carcinomas with serum levels exceeding 5000 ng/ml, but were absent in 17 tumours with serum AFP levels below 5000 ng/ml. All tumours other than hepatocellular carcinomas and hepatoblastomas were AFP negative. Carcinoembryonic antigen was present in 72% of cholangiocarcinomas, but was demonstrated in only one hepatocellular carcinoma. This exception was a combined hepatocellular-cholangiocarcinoma in which CEA expression was restricted to the cholangiocellular part. Alpha 1-antitrypsin was found in 4/63 hepatocellular carcinomas, in 2/2 fibrolamellar carcinomas and in 2/18 cholangiocarcinomas. Alpha-human chorionic gonadotropin was detected in one hepatocellular carcinoma and was strongly expressed in both fibrolamellar carcinomas. Weak staining for keratin was seen in most tumours with hepatocellular differentiation. All cholangiocarcinomas, in contrast, were strongly labelled with the keratin antibody. Co-expression of keratin and vimentin was observed in seven poorly differentiated hepatocellular carcinomas and three cholangiocarcinomas as well as in the two hepatoblastomas. The findings suggest that AFP is a diagnostic but rather insensitive immunocytochemical marker for hepatocellular differentiation in malignant liver tumours; CEA and keratin may help in discriminating cholangiocarcinomas from hepatocellular carcinomas.