Androgen receptors: a marker to increase sensitivity for identifying breast cancer in skin metastasis of unknown primary site.

Metastatic lesions to the skin may present a dilemma in the identification of the primary site. Breast carcinoma, metastatic to the skin, that is negative for estrogen receptors (ERs) and/or progesterone receptors (PRs) may be mimicked by a number of other metastatic lesions. In the present study, 16 formalin-fixed and paraffin-embedded infiltrating ductal carcinomas metastatic to the skin, which were ER-/PR-, ER-/PR+, or ER+/PR-; 5 metastatic lesions to the skin from primary lesions other than breast cancer; and 5 eccrine tumors were examined for immunoreactivity to the androgen receptor. The majority of the metastatic breast lesions (82%) exhibited immunopositivity for androgen receptor, whereas the metastatic skin lesions from primary lesions other than breast cancer and the eccrine tumors were immunonegative. Thus, androgen receptor immunohistochemistry could serve as a marker to increase sensitivity for identifying breast cancer in skin metastasis of unknown primary sites.     

Expression of PC-cell-derived growth factor in benign and malignant human breast epithelium

PC-cell-derived growth factor (PCDGF, progranulin) is a novel autocrine growth factor that is overexpressed in human breast cancer cell lines. We have examined immunohistochemical PCDGF expression in 206 paraffin-embedded human breast lesions and investigated its association with clinicopathological variables. PCDGF staining was observed in breast carcinoma, whereas it was almost always negative in benign breast epithelium. PCDGF expression was more common in invasive ductal carcinoma (80% cases positive) than in invasive lobular carcinoma (53% positive). PCDGF staining was almost never observed in lobular carcinoma in situ. Ductal carcinoma in situ expressed PCDGF in 66% of the cases, and this expression correlated strongly with nuclear grade. Similar correlation was observed between PCDGF expression and histologic grade of invasive ductal carcinoma. Average Ki-67 index of PCDGF-negative/weakly positive invasive carcinomas (30.3) was significantly lower than that of strongly PCDGF-positive tumors (48.8, P=0.01). A larger percentage of tumors that expressed PCDGF with a staining intensity of 2+ or 3+ were p53 positive (44%) than were PCDGF-negative tumors (25%), P=0.02. PCDGF expression was independent of c-erbB-2 overexpression and of ER and PR status. Our study provides the first evidence of high incidence of PCDGF expression in human breast cancer in which it correlates with clinicopathological variables such as tumor grade, proliferation index, and p53 expression. These characteristics, as well as the virtual absence of expression in benign breast tissue, suggest an important role of PCDGF in breast cancer pathogenesis and make it a potential novel target for the treatment of breast cancer.     

Expression of EGFR family and steroid hormone receptors in ductal carcinoma in situ of the breast.

The expression of EGFR family and steroid hormone receptors was examined in a series of 40 cases of pure ductal carcinoma in situ (DCIS) of the breast by immunohistochemical staining of paraffin-embedded sections. Hematoxylin and eosin-stained sections were used to classify the tumors according to the published criteria by Holland et al. (Holland R, Peterse JL, Millis RR, et al. Semin Diagn Pathol. 1994;1 1:167-180). Of the tumors 48% were immunoreactive for EGFR, 63% for c-erbB-2, 78% for c-erbB-3, 95% for c-erbB-4, 88% for estrogen receptor (ER) and 80% for progesterone receptor (PR). Statistically significant association between histological grade (differentiation) and c-erbB-2 protein expression was seen (p <.001). In addition, expression of c-erbB-4 protein was associated with c-erbB-2 (p=.004), c-erbB-3 (p=.058), ER (p=.002) and PR (p=.004). It is concluded that c-erbB-2 expression in DCIS is associated with high-grade pathological features, and a higher c-erbB-2 expression is seen in DCIS than in invasive breast carcinomas. A possible association between extensive expression of c-erbB-4 and steroid hormone receptors in proliferative and premalignant breast epithelial cells and the c-erbB-2 expression in DCIS and invasive breast carcinomas is discussed.     

Expression of EGFR Family and Steroid Hormone Receptors in Ductal Carcinoma in situ of the Breast

The expression of EGFR family and steroid hormone receptors was examined in a series of 40 cases of pure ductal carcinoma in situ (DCIS) of the breast by immunohistochemical staining of paraffin-embedded sections. Hematoxylin and eosin-stained sections were used to classify the tumors according to the published criteria by Holland et al. (Holland R, Peterse JL, Millis RR, et al. Semin Diagn Pathol. 1994;11:167-180). Of the tumors 48% were immunoreactive for EGFR, 63% for c-erbB-2, 78% for c-erbB-3, 95% for c-erbB-4, 88%for estrogen receptor (ER) and 80% for progesterone receptor (PR). Statistically significant association between histological grade (differentiation) and c-erbB-2 protein expression was seen ( p <.001). In addition, expression of c-erbB-4 protein was associated with c-erbB-2 ( p =.004), c-erbB-3 ( p =.058), ER ( p =.002) and PR ( p =.004). It is concluded that c-erbB-2 expression in DCIS is associated with high-grade pathological features, and a higher c-erbB-2 expression is seen in DCIS than in invasive breast carcinomas. A possible association between extensive expression of c-erbB-4 and steroid hormone receptors in proliferative and premalignant breast epithelial cells and the c-erbB-2 expression in DCIS and invasive breast carcinomas is discussed.     

Evaluation of androgen receptor and GATA binding protein 3 as immunohistochemical markers in the diagnosis of metastatic breast carcinoma to the lung

Differentiating metastatic breast carcinoma in the lungs from primary lung tumors and mesotheliomas is important for determining prognosis and treatment. We evaluated novel breast specific markers, androgen receptor (AR) and GATA binding protein 3 (GATA3) immunohistostaining, for this differential, and compare to other traditional markers. The specimens comprised 33 metastatic breast carcinomas to the lung, 566 primary lung tumors (170 adenocarcinomas, 157 squamous cell carcinomas, 31 pleomorphic carcinomas, 115 large cell neuroendocrine carcinomas, 43 small cell carcinomas, and 49 typical carcinoids) and 42 malignant mesotheliomas. They were analyzed by immunohistochemistry using antibodies to AR, GATA3, estrogen receptor (ER), progesterone receptor (PgR), mammaglobin, gross cystic disease fluid protein‐15 (GCDFP‐15). Of the metastatic breast carcinomas, immunohistostaining of AR, GATA3, ER, PgR, mammaglobin, GCDFP‐15 were positive in 27 cases (81.8%), 24 cases (72.7%), 26 cases (78.8%), 13 cases (39.4%), 12 cases (36.4%), 9 cases (27.3%), respectively. Of primary lung tumors and mesotheliomas, staining of AR, GATA3, ER, PgR, mammaglobin, GCDFP‐15 were positive in 18 cases (3%), 3 cases (0.5%), 4 cases (0.7%), 2 cases (0.3%), 0 case (0%), 2 cases (0.3%), respectively. Immunohistochemistry of AR and GATA3 are reliable for differentiating metastatic breast carcinoma from primary lung tumors and mesotheliomas.     

S-100 immunoreactivity in primary and metastatic carcinoma of the breast: a potential source of error in immunodiagnosis

Immunoreactivity for S-100 protein, typically a marker for malignant melanoma and neural-derived tumors, was observed in neoplastic cells of 57 of 68 cases (84%) of formalin-fixed, paraffin-embedded primary and/or metastatic carcinoma of the breast of various histologic types. The extent of S-100 immunoreactivity varied, with only a minor proportion of positive tumor cells noted in some cases. An awareness of this staining profile for S-100 protein, particularly in metastatic poorly differentiated neoplasms with unknown primaries, is imperative for accurate immunohistochemical interpretation. Using a panel of reagents which includes antibodies to keratin proteins and epithelial membrane antigen, the epithelial nature of S-100-positive carcinomas may be readily defined. Tumor cells in all cases of primary and metastatic carcinoma of the breast evaluated in this study exhibited strong staining for both of these tissue markers. To preclude misinterpretation of tumor type due to anomalous staining patterns for a specific antibody, eg, S-100 protein, a panel of antibodies is recommended for assessment of metastatic poorly differentiated tumors.     

Immunocytochemical localization of carcinoembryonic antigen in cerebrospinal fluid with metastatic carcinoma of the stomach: report of four cases

A study was undertaken to evaluate the cellular findings of gastric carcinoma in cerebrospinal fluid (CSF). Immunocytochemical localization of carcinoembryonic antigen (CEA) was performed on four cases of metastatic gastric carcinoma cells in CSF samples. A positive peroxidase-antiperoxidase (PAP) reaction was obtained in all cases, with intense staining for CEA in the CSF samples as well as in the paraffin-embedded tissue sections from the primary gastric tumors. Cellular morphology and the results of immunoperoxidase staining can be studied simultaneously. We believe that the PAP method for CEA increases diagnostic accuracy of cytology in the CSF.     

Epidermal growth factor, estrogen, and progesterone receptor expression in primary sweat gland carcinomas and primary and metastatic mammary carcinomas.

The distinction between primary sweat gland carcinomas and metastatic breast carcinoma to the skin is sometimes difficult. In an effort to improve this discrimination, we compared the immunohistochemical staining pattern of 42 primary sweat gland carcinomas (SGCs) with 30 metastases from breast carcinoma (BC) to the skin, 125 primary BCs, and 30 noncutaneous metastases from BCs. The antibodies used were against the receptors for epidermal growth factor (EGF-R), estrogen receptor (ER), and progesterone receptor (PR). The frequencies of positive staining were as follows for EGF-R: 34 (81%) of 42 SGCs, 5 (17%) of 30 BCs metastatic to skin, 28 (22%) of 125 primary BCs, and 6 (20%) of 30 noncutaneous BC metastases. For ER, the frequencies were 9 (21%) of 42 SGCs and 10 (33%) of 30 BCs metastatic to skin. The frequencies for PR were 8 (19%) of 42 SGCs and 8 (27%) of 30 BCs metastatic to skin. These results suggest that expression of EGF-R may be diagnostically helpful, because it is strongly associated with SGCs when compared with metastatic BCs (P < .0001). This association is also present when ductal eccrine and apocrine types of SGC, which are the histologic subtypes of SGC most difficult to distinguish from metastatic BC, are separately analyzed (P < .001). The frequencies of expression of ER and PR in SGCs and BCs metastatic to skin were not significantly different.     

Oestrogen receptors in benign epithelial lesions and intraduct carcinomas of the breast: an immunohistological study

We examined 198 breast lesions, representing commonly encountered benign epithelial proliferative disorders, lobular carcinoma in situ and intraduct carcinoma, immunohistologically for oestrogen receptors (ER). A mixture of three ER monoclonal antibodies--H222, D75 and D547--was used on sections of routinely processed and paraffin-embedded tissue blocks. Over 65% of the benign and malignant lesions showed some evidence of ER expression and significant staining was recorded by two observers in 28-31% of fibroadenomas, 18-28% of ductal epithelial hyperplasias, 30-40% of sclerosing adenosis cases, 38-45% of papillomas, 60% of in situ lobular carcinomas and 42-45% of intraduct carcinomas. Apocrine metaplastic cells and myoepithelial cells showed absent or only weak staining. Amongst intraduct carcinomas, less than 20% of comedo carcinomas and over 50% of cribriform, papillary and solid variants showed significant ER staining.     

Reliability of Her2/neu, estrogen receptor, and progesterone receptor testing by immunohistochemistry on cell block of FNA and serous effusions from patients with primary and metastatic breast carcinoma

The prognostic and predictive value of Her2/neu and the hormone receptors in patient with primary or metastatic breast cancer is essential for a favorable outcome of treatment. We have been experiencing increasing requests to test cytologic specimens for these markers in patients with metastatic breast carcinoma. A recent study threw some doubts on the validity of such testing using cell blocks. In this study we compared our immunohistochemical Her2/neu, ER and PR testing performed on 42 formalin-fixed, paraffin-embedded cell blocks from 27 fine needle aspirations (FNA) and 15 serous effusions of 42 patients with metastatic (n = 38) and primary (n = 4) breast carcinoma to the test results obtained on tissue sections. In seven cases the Her2/neu immunohistochemistry (IHC) results on cell blocks were also compared with Her2/neu fluorescence in situ hybridization (FISH) on tissue or cell block. The study revealed 100% correlation for positive and negative Her2/neu results. For ER testing the results showed 85.7% sensitivity, 100% specificity, 100% positive predictive value (PPV), and 85.7% negative predictive value (NPV). For PR testing the results showed 80% sensitivity, 100% specificity, 100% PPV, and 88.8% NPV respectively. In conclusion, IHC for Her2/neu, ER and PR performed on formalin-fixed, paraffin-embedded cell blocks prepared from fresh FNA and serous fluid is reliable in predicting the expression of these markers when correlated with IHC and FISH performed on the corresponding tumor tissue.     

Immunohistochemical evaluation of estrogen and progesterone receptor content in 183 patients with endometrial carcinoma. Part I: Clinical and histologic correlations.

A series of 183 cases of primary endometrial carcinomas were immunohistochemically stained for estrogen receptors (ERs) and progesterone receptors (PRs) using formalin-fixed, paraffin-embedded sections. All specimens were obtained from uterine curettages performed at the time of the initial diagnosis or initial therapy. The ER and PR content in the malignant and benign components (benign epithelium, stroma, and myometrium) was evaluated separately for positivity and divided into three groups according to the percentage of positive cells and the intensity of the nuclear stain. Endometrioid-type adenocarcinoma had the highest degree of positivity for both receptors, followed by adenosquamous carcinoma, serous carcinoma, and clear cell carcinoma. The positivity for ERs and PRs of the malignant component was statistically correlated with the International Federation of Gynecology and Obstetrics (FIGO) stage (P less than 0.01), FIGO grade (P less than 0.001), and nuclear grade (P less than 0.0001) of the tumors. The degrees of ER and PR positivity of the malignant component correlated with each other (P less than 0.0001). There was no association between the depth of myometrial tumor invasion and either receptor status of the malignant component. There was a significant association between the presence of lymph vessel invasion and the positivity for PR. Positivity for PR correlated negatively with the patients' ages (P less than 0.004). The results of this study indicate that immunohistochemical analysis of sex steroid receptor status on formalin-fixed, paraffin-embedded tissue offers an excellent alternative to the standard biochemical procedure.     

D2-40: an additional marker for myoepithelial cells of breast and the precaution in interpreting tumor lymphovascular invasion

D2-40 is a recently available mouse monoclonal antibody specific for human podoplanin and has been used in identifying lymphovascular invasion (LVI) of tumors. Although its expression has been evaluated in other tissues, its use as a marker for myoepithelial cells (MEC) of breast has not been studied. To explore its expression in the MEC of breast, paraffin-embedded tissue blocks from 48 patients with breast diseases were selected to include usual ductal hyperplasia (UDH, 41 cases), atypical ductal hyperplasia (ADH, 4 cases) and ductal carcinoma in situ (DCIS, 17 cases). Normal breast parenchyma and invasive carcinoma coexisting in the tissue sections were also included in the study. Immunohistochemistry for D2-40, calponin and p63 was performed and the staining patterns were reviewed and compared. D2-40 immunohistochemical staining is positive in the cytoplasm of MEC in UDH, ADH, and the majority of DCIS. The staining pattern of D2-40 is comparable with that of calponin, however D2-40 staining of MEC is weaker than that of calponin and with less background. In addition, myoepithelial cells and myofibroblasts at the edge of retraction spaces of DCIS are also stained by D2-40 that could be misinterpreted as tumor LVI. In conclusion, D2-40 immunohistochemistry reliably identifies the MEC of breast in a variety of lesions in a pattern similar to that of calponin and p63, and can be used as an additional MEC marker. Caution should be exercised when interpreting the staining of cells surrounding DCIS and carcinoma with retraction artifact.     

Hyaluronan in peritumoral stroma and malignant cells associates with breast cancer spreading and predicts survival

Hyaluronan (HA) is an extracellular matrix polysaccharide that promotes cell migration through its cell surface receptors and by effecting changes in the physical environment. HA expression is frequently increased in malignant tumors, whereas its association with the invasive potential and patient outcome in breast cancer has not been reported. The localization and signal intensity of HA was analyzed in 143 paraffin-embedded tumor samples of human breast carcinoma using a biotinylated HA-specific probe. In the immediate peritumoral stroma, HA signal was moderately or strongly increased in 39% and 56% of the cases, respectively. Normal ductal epithelium showed no HA, whereas in 57% of the tumors at least some of the carcinoma cells were HA positive. The intensity of the stromal HA signal and the presence of cell-associated HA were both significantly related to poor differentiation of the tumors, axillary lymph node positivity, and short overall survival of the patients. In Cox's multivariate analysis, both the intensity of stromal HA signal alone and that combined with the HA positivity in tumor cells were independent prognostic factors for overall survival. These results suggest that HA is directly involved in the spreading of breast cancer and may offer a potential target for new therapies.     

Study of neu-protein expression in mammary Paget's disease with and without underlying breast carcinoma and in extramammary Paget's disease.

Correlation between neu/c-erbB-2/Her-2 gene amplification and overexpression of the neu gene product has been reported in tumors of glandular origin, especially ductal breast carcinomas. Formalin-fixed and dewaxed sections from 23 cases of mammary (MPD) and 9 cases of extramammary (EPD) Paget's disease were immunohistochemically stained by means of the monoclonal antibody 3B5 directed against an intracellular domain of the neu gene protein. All MPDs exhibited a distinct membrane staining of tumor cells independent of the presence of ductal breast carcinomas found in 18 cases. All these breast carcinomas also were positive for neu staining. In contrast to MPD, all EPDs were negative. Normal epidermis was always negative. Northern blot analysis sustained the immunohistologic findings in that the presence of neu mRNA could be demonstrated in two of three cases with MPD. Negativity in one case was due to dilution effects by nontumor cells. Our results suggest that Paget cells of mammary and extramammary localization, although very similar phenotypically, derive from different genetic accidents. Furthermore neu positivity in all MPDs and all underlying ductal carcinomas suggests common genetic alterations for both tumors. However the finding of five neu protein-positive MPDs without associated ductal breast carcinomas may suggest a somewhat different transformation process.     

Adenoid cystic carcinoma of the breast: a tumour commonly devoid of oestrogen receptors and related proteins

AIM: Adenoid cystic carcinoma (ACC) of the breast is an uncommon well-differentiated tumour with good prognosis, and sometimes difficult to distinguish from in-situ and invasive cribriform carcinoma (ICC) which are relatively more common. Recently, we encountered a case of ACC that proved to be totally oestrogen receptor (ER) negative by immunohistochemistry. We investigated the possibility that this may be a consistent feature that can help in differentiating ACC from ICC which are usually ER positive. METHODS AND RESULTS: The immunoperoxidase technique was used to study the expression of ER and other related proteins in six cases of ACC and two cases of ICC. All ACC cases were negative for oestrogen (ER) and progesterone (PgR) receptors whereas the two ICC were strongly positive for ER and showed a variable degree of PgR positivity. In addition, ACC cases were pS2 negative and showed minimal expression of prolactin receptors (PrlR), while the two ICC showed widespread and strong staining for pS2 and PrlR. The percentages of cells staining positively for Ki67 and p27 were generally lower in ACC than in ICC. Both tumour types were c-erbB-2 negative, but p53 was weakly to moderately positive. CONCLUSIONS: The findings suggest that a negative immunoperoxidase staining for ER would confirm the diagnosis of ACC in contrast to the positive staining which is always seen in ICC. The findings also raise the issue of the presence of a specific class of ER negative breast carcinomas which are negative not because of poor differentiation, but because of their derivation from, or differentiation along, an ER negative cell lineage.     

Immunocytochemical assay of progesterone receptors in paraffin-embedded specimens of endometrial carcinoma and hyperplasia: a preliminary evaluation

An immunohistochemical method for the detection of progesterone receptors (PgR) using the monoclonal anti-PgR antibody KD 68 was utilized to study paraffin-embedded tissue sections from women with endometrial carcinoma and hyperplasia. Stromal as well as myometrial nuclear PgR were nearly always apparent. In carcinoma, 11/24 (46%) of cases showed epithelial positivity, whereas in hyperplasia 8/9 (89%) were PgR-positive (P less than 0.05). Initial biochemical PgR assays by the dextran-coated charcoal method were compared with results of PgR-immunocytochemical assays (ICA) in the paraffin-embedded tissue and were in concordance in 92%. In the one discordant specimen, PgR-ICA-negative tumor cells were seen infiltrating PgR-ICA-positive myometrium, and the biochemical assay was thus felt to be falsely positive. Twelve additional cases of endometrial carcinoma were also studied for estrogen receptor (ER) by immunocytochemistry. Two were positive for both ER and PgR, while five were negative for both receptors. The immunocytochemical methods described allow for analysis of routinely fixed, paraffin-embedded specimens, thus permitting analysis of very small specimens and archival material.     

Expression of p63 in primary cutaneous adnexal neoplasms and adenocarcinoma metastatic to the skin.

p63, a recently identified homologue of the p53 gene, has been reported to be essential in the development of epithelia and is mainly expressed by basal and myoepithelial cells. The purpose of this study was to investigate the pattern of p63 expression in cutaneous adnexal neoplasms and to assess its possible value in the differential diagnosis of primary cutaneous neoplasms vs adenocarcinomas metastatic to the skin. Immunohistochemical analysis for p63 was performed on formalin-fixed, paraffin-embedded archival tissue from 20 benign adnexal tumors, 10 malignant adnexal tumors and 14 adenocarcinomas metastatic to the skin. The expression of p63 was evaluated in epidermal cells, skin appendages and metastatic tumor cells. p63 was consistently expressed in the basal and suprabasal cells of epidermis and cutaneous appendages, including the basal/myoepithelial cells of sweat glands. Out of 20 benign adnexal tumors, 13 (65%) showed strong (score 3) p63 expression; the remaining seven (35%) cases had score 2. All primary cutaneous carcinomas, including adenocarcinomas, expressed p63. In contrast, none of the metastatic adenocarcinomas to the skin was positive for p63 (P<0.001). Based on our findings, analysis of p63 expression may help in the differential diagnosis of primary vs metastatic cutaneous adenocarcinomas.     

Immunohistochemical determination of HER-2/neu expression in invasive breast carcinoma

Numerous methods exist for HER-2/neu assessment; however, technical and interpretive standardization is virtually absent. We evaluated 2 commercially available antibodies on routinely fixed paraffin-embedded tissue sections to establish our own guidelines. Thirty-three cases of infiltrating breast carcinoma were evaluated simultaneously with monoclonal and polyclonal antibodies. Only membranous staining, no matter how focal, was considered positive. An additional 32 tumors were studied subsequently using only the polyclonal antibody. Of all carcinomas, 13.0% showed immunohistochemical evidence of HER-2/neu overexpression. High-grade tumors were more often positive. There was no HER-2/neu gene expression in the benign epithelium that generally was present in the tissue section or in any of the well-differentiated tumors tested. The polyclonal antibody proved more sensitive than the monoclonal antibody. While true cytoplasmic staining was present occasionally, it did not create substantial difficulty in interpretation. The polyclonal antibody cost substantially less than the monoclonal antibody. Fluorescence in situ hybridization assay for HER-2/neu gene amplification performed on 32 of 65 cases showed concordant results in 31 cases. The immunohistochemical assay for HER-2/neu gene overexpression, using our methods, is accurate, economic, and easily integrated into the laboratory.     

An evaluation of potentially suitable fixatives for immunoperoxidase staining of estrogen receptors in imprints and frozen sections of breast carcinoma

The estrogen receptor (ER) content of breast carcinoma is generally accepted as valuable in predicting clinical outcome and tumour response to hormonal manipulation. We applied a new immunocytochemical assay for estrogen receptors (Abbott ERICA Monoclonal) to 20 breast tumours, and examined the efficacy of 16 fixation procedures before immunoperoxidase staining of frozen sections and imprint preparations. Our findings indicate that the fixatives of choice are periodatelysine-paraformaldehyde at 22 degrees C, or 10% formalin followed by acetone at -10 degrees C. These fixation procedures are simpler, less time-consuming, and provide superior staining, tumour cytomorphology and higher ER values than the 3-reagent sequence recommended by Abbott Laboratories. There was a significant correlation between the ER scores in the frozen sections and the imprints. Positive ER cytosol results correlated with the staining index in the frozen sections, and the ER scores in the imprints. We conclude that imprints are suitable preparations for ER analysis by the immunoperoxidase technique, particularly for small tumour specimens.     

The role of cytokeratins 20 and 7 and estrogen receptor analysis in separation of metastatic lobular carcinoma of the breast and metastatic signet ring cell carcinoma of the gastrointestinal tract

Metastatic signet ring cell carcinomas of unknown primary site can represent a clinical problem. Gastrointestinal signet ring cell carcinomas and invasive lobular carcinomas of the breast are the most common sources of these metastases. Immunohistochemical algorithms have been successfully used in the search for the unknown primary adenocarcinomas. In the present study a series of primary invasive lobular breast carcinomas (79 cases) and their metastases and a series of gastrointestinal signet ring cell carcinomas (22 primary and 13 metastases) were stained with monoclonal antibodies for cytokeratin (CK) 20 and CK7 and for estrogen receptors (ER). The staining was evaluated as negative (no staining), focally (less than 10% of the tumor cells stained) or diffusely positive. All the primary and metastatic gastrointestinal signet ring cell carcinomas proved to be CK20 positive, while only 2/79 (3%) of the primary and 1/21 metastatic lobular carcinomas (5%) stained positively for this CK. None of the gastrointestinal carcinomas and the majority of the lobular carcinomas expressed ER. The majority of the tumors were CK7+. Using CK20 alone, 33 of 34 metastases could be properly classified as gastrointestinal (CK20+) or mammary (CK20-). ER identified 31/34 of breast cancer metastases. By combining the results of CK20 and ER staining all the metastases could be properly classified as the CK20+/ER- pattern identified all the gastrointestinal tumors.