Immunocytochemical double staining of cytokeratin and prostate specific antigen in individual prostatic tumour cells

Liquid biopsy for monitoring of tumor dormancy and early detection of disease recurrence in solid tumors

Cancer is one of the three leading causes of death worldwide. Even after successful therapy and achieving remission, the risk of relapse often remains. In this context, dormant residual cancer cells in secondary organs such as the bone marrow constitute the cellular reservoir from which late tumor recurrences arise. This dilemma leads the term of minimal residual disease, which reflects the presence of tumor cells disseminated from the primary lesion to distant organs in patients who lack any clinical or radiological signs of metastasis or residual tumor cells left behind after therapy that eventually lead to local recurrence. Disseminated tumor cells have the ability to survive in a dormant state following treatment and linger unrecognized for more than a decade before emerging as recurrent disease. They are able to breakup their dormant state and to readopt their proliferation under certain circumstances, which can finally lead to distant relapse and cancer-associated death. In recent years, extensive molecular and genetic characterization of disseminated tumor cells and blood-based biomarker has contributed significantly to our understanding of the frequency and prevalence of tumor dormancy. In this article, we describe the clinical relevance of disseminated tumor cells and highlight how latest advances in different liquid biopsy approaches can be used to detect, characterize, and monitor minimal residual disease in breast cancer, prostate cancer, and melanoma patients.

Identifying cancer origin using circulating tumor cells

Circulating tumor cells (CTCs) have become an established clinical evaluation biomarker. CTC count provides a good correlation with the prognosis of cancer patients, but has only been used with known cancer patients, and has been unable to predict the origin of the CTCs. This study demonstrates the analysis of CTCs for the identification of their primary cancer source. Twelve mL blood samples were equally dispensed on 6 CMx chips, microfluidic chips coated with an anti-EpCAM-conjugated supported lipid bilayer, for CTC capture and isolation. Captured CTCs were eluted to an immunofluorescence (IF) staining panel consisting of 6 groups of antibodies: anti-panCK, anti-CK18, anti-CK7, anti-TTF-1, anti-CK20/anti-CDX2, and anti-PSA/anti-PSMA. Cancer cell lines of lung (H1975), colorectal (DLD-1, HCT-116), and prostate (PC3, DU145, LNCaP) were selected to establish the sensitivity and specificity for distinguishing CTCs from lung, colorectal, and prostate cancer. Spiking experiments performed in 2mL of culture medium or whole blood proved the CMx platform can enumerate cancer cells of lung, colorectal, and prostate. The IF panel was tested on blood samples from lung cancer patients (n = 3), colorectal cancer patients (n = 5), prostate cancer patients (n = 5), and healthy individuals (n = 12). Peripheral blood samples found panCK⁺ and CK18⁺ CTCs in lung, colorectal, and prostate cancers. CTCs expressing CK7⁺ or TTF-1⁺, (CK20/ CDX2)⁺, or (PSA/ PSMA)⁺ corresponded to lung, colorectal, or prostate cancer, respectively. In conclusion, we have designed an immunofluorescence staining panel to identify CTCs in peripheral blood to correctly identify cancer cell origin.

Combined genome and transcriptome analysis of single disseminated cancer cells from bone marrow of prostate cancer patients reveals unexpected transcriptomes

Bone is the most frequent site of metastasis in prostate cancer and patients with bone metastases are deemed incurable. Targeting prostate cancer cells that disseminated to the bone marrow before surgery and before metastatic outgrowth may therefore prevent lethal metastasis. This prompted us to directly analyze the transcriptome of disseminated cancer cells (DCC) isolated from patients with nonmetastatic (UICC stage M0) prostate cancer. We screened 105 bone marrow samples of patients with M0-stage prostate cancer and 18 bone marrow samples of patients without malignancy for the presence of EpCAM(+) single cells. In total, we isolated 270 cells from both groups by micromanipulation and globally amplified their mRNA. We used targeted transcriptional profiling to unambiguously identify DCCs for subsequent in-depth analysis. Transcriptomes of all cells were examined for the expression of EPCAM, KRT8, KRT18, KRT19, KRT14, KRT6a, KRT5, KLK3 (PSA), MAGEA2, MAGEA4, PTPRC (CD45), CD33, CD34, CD19, GYPC, SCL4A1 (band 3), and HBA2. Using these transcripts, we found it impossible to reliably identify true DCCs. We then applied combined genome and transcriptome analysis of single cells and found that EpCAM(+) cells from controls expressed transcripts thought to be epithelial-specific, whereas true DCCs may express hematopoietic transcripts. These results point to an unexpected transcriptome plasticity of epithelial cancer cells in bone marrow and question common transcriptional criteria to identify DCCs.

Detection of circulating tumor cells in prostate cancer patients: methodological pitfalls and clinical relevance

Disseminated malignancy is the major cause of prostate cancer-related mortality. Circulating tumor cells (CTCs) are essential for the establishment of metastasis. Various contemporary and molecular methods using prostate-specific biomarkers have been applied to detect extraprostatic disease that is undetectable by conventional imaging techniques, assessing the risk for disease recurrence after therapy of curative intent. However, the clinical relevance of CTC detection is still controversial. We review current literature regarding molecular methods used for the detection of CTCs in the peripheral blood and bone marrow biopsies of patients with prostate cancer, and we discuss the methodological pitfalls that influence the clinical significance of molecular staging.

The urokinase receptor (u-PAR)--a link between tumor cell dormancy and minimal residual disease in bone marrow?

Minimal residual disease (MRD) is hypothesized to be the major cause of tumor recurrence and metastasis even years and decades after primary cancer diagnosis and curative solid tumor resection. In these patients disseminated tumor cells reflecting MRD can be detected in the bone marrow years after treatment. It is to be assumed that genetic determinants and a complex interplay between the disseminated tumor cells and their microenvironment in the bone marrow are responsible for tumor cell dormancy and the final reactivation towards metastasis. The urokinase receptor (u-PAR), a critical regulator of invasion, intravasation, and metastasis, is found to be a key player in regulating the shift between single cell tumor dormancy and proliferation. This has mainly been attributed to a regulation by u-PAR of integrins, and the ability of the latter to propagate signals from fibronectin through the EGF-receptor, ERK, and p38 signaling. Interestingly, u-PAR is found in disseminated tumor cells in the bone marrow of solid cancer patients, and is associated with the expansion of these cells and clinical prognosis. Here we summarize and discuss findings on disseminated tumor cells in the bone marrow, MRD and the role of u-PAR in tumor biology, especially focusing on its specific role in providing a switch between tumor cell proliferation and dormancy. Finally, we discuss the hypothesis that u-PAR might be an essential molecule in bone marrow disseminated tumor cells for long-term survival during dormancy, and/or reactivation of their proliferation years after primary treatment.

Review: Biological relevance of disseminated tumor cells in cancer patients

The prognosis of cancer patients is largely determined by the occurrence of distant metastases. In patients with primary tumors, this relapse is mainly due to clinically occult micrometastasis present in secondary organs at primary diagnosis but not detectable even with high resolution imaging procedures. Sensitive and specific immunocytochemical and molecular assays enable the detection and characterization of disseminated tumor cells (DTC) at the single cell level in bone marrow (BM) as the common homing site of DTC and circulating tumor cells (CTC) in peripheral blood. Because of the high variability of results in DTC and CTC detection, there is an urgent need for standardized methods. In this review, we will focus on BM and present currently available methods for the detection and characterization of DTC. Furthermore, we will discuss data on the biology of DTC and the clinical relevance of DTC detection. While the prognostic impact of DTC in BM has clearly been shown for primary breast cancer patients, less is known about the clinical relevance of DTC in patients with other carcinomas. Current findings suggest that DTC are capable to survive chemotherapy and persist in a dormant nonproliferating state over years. To what extent these DTC have stem cell properties is subject of ongoing investigations. Further characterization is required to understand the biology of DTC and to identify new targets for improved risk prevention and tailoring of therapy. Our review will focus on breast, colon, lung, and prostate cancer as the main tumor entities in Europe and the United States.

Prognostic relevance of disseminated tumour cells in bone marrow of patients with transitional cell carcinoma

OBJECTIVE

This prospective study is the first immunocytochemical investigation of the frequency and prognostic value of CK+ tumour cells in the bone marrow of patients with transitional cell carcinoma (TCC).

METHODS

Bone marrow aspirates from 228 TCC patients were taken preoperatively. Cytospins were made and stained by immunocytochemistry using the monoclonal antibodies CK2 and A45-B/B3. 27 patients with no evidence of any malignant disease served as control group.

RESULTS

CK+ tumour cells were detected in 28% (63/228) of the TCC patients. No CK+ cells (0/27) were detected in the control group. In multivariate analysis the detection of > or =3 CK+ cells in bone marrow was an independent prognostic factor (hazard ratio=2.7, p<0.05) in patients with T2-4 tumour classification.

CONCLUSION

Disseminated CK+ cells play a role in the biology of tumour spread of TCC, and their immunocytochemical detection can be useful in assessing the prognosis of TCC patients with an invasive tumour.

Early metastasis of human solid tumours: expression of cell adhesion molecules

Loss and gain of cell surface molecules determines the mobilization, emigration and invasiveness of epithelial cancer cells. As a first approach to gain further insight into these processes, we have followed two strategies: (1) to identify tumour cells which have disseminated early from primary carcinomas and to obtain information about the phenotype and prognostic significance of these cells; and (2) to identify molecular changes occurring in primary tumour cells at the time they develop their metastatic potential. Our analyses indicate that changes in the adhesive properties of solid tumour cells, such as down-regulation of desmosomal proteins (e.g. plakoglobin) and neo-expression of ICAM-1 or MUC18, are important determinants of the metastatic capability of individual malignant cells. The expression pattern of these cell adhesion molecules during tumour progression appears to reflect a disturbance at the level of the molecular elements normally responsible for controlling their expression. The outlined current strategies for detection, characterization and antibody therapy of cancer micrometastasis can be applied to the secondary prevention of metastatic disease in patients with minimal residual cancer.

The detection and isolation of viable prostate-specific antigen positive epithelial cells by enrichment: a comparison to standard prostate-specific antigen reverse transcriptase polymerase chain reaction and its clinical relevance in prostate cancer

PURPOSE

To isolate prostate epithelial cells from the peripheral blood and bone marrow, and compare prostate-specific antigen (PSA) reverse transcriptase polymerase chain reaction (RT-PCR) performed on unenriched or epithelial enriched peripheral blood and bone marrow samples.

PATIENTS AND METHODS

Peripheral blood samples from 371 patients with prostate cancer and 141 controls, and bone marrow samples from 292 patients with prostate cancer and 43 controls were obtained. One aliquot was assessed with PSA RT-PCR. Another was enriched for epithelial cells with paramagnetic immune microbeads and assessed for: (1) PSA immunohistochemistry, (2) PSA RT-PCR, and (3) immunofluorescent detection of epithelial cells.

RESULTS

In the bone marrow (P < 0.01), but not the peripheral blood (P = 0.62), we observed significantly higher detection rates of disseminated PSA expressing epithelial cells after enrichment. The presence of epithelial cells with or without evidence of PSA production was uncommon among controls both in peripheral blood (1% and 0%) and bone marrow (11% and 0%). In patients with active prostate cancer, 46% to 74% had epithelial cells in peripheral blood, and 20% to 64% had PSA expressing epithelial cells. In bone marrow, 55% to 92% had epithelial cells, and 43% to 83% had PSA expressing epithelial cells. Particularly in bone marrow, circulating cells were frequently detected in men without evidence of disease after prostatectomy. With limited follow-up, the detection of epithelial cells or PSA expressing epithelial cells in peripheral blood or bone marrow before radical prostatectomy does not define a population of patients that will have biochemical failure.

CONCLUSIONS

Immunomagnetic enrichment frequently detects epithelial, presumably malignant, cells in the peripheral blood and, especially, the bone marrow of patients with prostate cancer. Viable cells can be acquired for gene expression and phenotyping studies.

Detection of tumor-specific DNA in blood and bone marrow plasma from patients with prostate cancer

Tumor tissues, blood plasma and bone marrow (BM) aspirates of 57 prostate cancer patients (PCa) without clinical signs of overt metastases were assessed for LOH (loss of heterozygosity) by a PCR-based fluorescence microsatellite analysis, using a panel of 15 markers. Additionally, micrometastatic tumor cells in BM were monitored by an immunocytological cytokeratin assay. In total, 25 (44%), 32 (56%) and 41 (72%) of the patients had at least 1 LOH in their blood, BM and tumor samples, respectively. Among the informative cases, the frequency of LOH was highest in blood plasma for the markers D8S360 (18%) and D10S1765 (15%), and in BM plasma for THRB (24%) and D8S137 (22%). Comparison of blood plasma and BM with tumors showed discrepant results in 35% and 45% of patients, respectively. Whereas all LOHs at THRB in BM plasma were also detected in the autologous tumor tissues, LOHs at D6S474 and D11S898 in BM were not retrieved in the tumors. The comparison with established risk factors showed a correlation of borderline significance for LOH at D9S1748 in the BM aspirates (p=0.055) and a significant correlation in the tumor samples (p=0.004) with increasing pathologic Gleason scores. Interestingly, 22% of the PCa patients harbored tumor cells in their BM and tended (p=0.065) to have more frequent LOH (16%) in BM plasma compared to patients without tumor cells (9%). These data demonstrate, for the first time, the presence of free tumor-specific DNA in blood and BM of PCa patients and suggest a possible relationship to BM micrometastasis.

Frequency and prognostic relevance of disseminated tumor cells in bone marrow of patients with metastatic renal cell carcinoma

BACKGROUND

The prognostic relevance of disseminated cytokeratin-positive (CK+) tumor cells in the bone marrow of patients with different types of carcinoma has been demonstrated in several studies. In this prospective study, the frequency and prognostic value of CK+ tumor cells was investigated in the bone marrow of 55 consecutive patients with metastatic renal cell carcinoma (M1 RCC) in comparison with 256 M0 RCC patients from a previous study.

METHODS

Aspiration of bone marrow from the anterior iliac crest was performed immediately before tumor resection in RCC patients. Cytospins were made and stained by immunocytochemistry using the APAAP (alkaline phosphatase-antialkaline phosphatase) protocol and monoclonal antibodies CK2 and A45-B/B3. Twenty-seven patients with no evidence of any malignant disease served as a control group.

RESULTS

CK+ tumor cells were detected in 42% (23 of 55 patients) of the M1 patients and 25% (63 of 256 patients) of the M0 patients (P <.01). No CK+ cells (0 of 27 patients) were detected in the control group. In the M1 group, CK- patients demonstrated a trend toward a better outcome compared with CK+ patients (log-rank test, P = .19). This difference was significant when applying a higher threshold (0-2 CK+ cells vs. > or = 3 CK+ cells; P <.05). On multivariate analysis, the detection of > or = 3 CK+ cells in the bone marrow was found to be an independent prognostic factor (P <.001).

CONCLUSIONS

The results of the current study indicate that disseminated CK+ cells play a role in the biology of tumor spread of RCC, and that their immunocytochemical detection can be useful in assessing the prognosis of patients with M1 disease.

Evaluation of bone marrow in breast cancer patients: prediction of clinical outcome and response to therapy

Blood-borne distant metastasis is the leading cause of cancer-related death in breast cancer. The onset of this fundamental process can now be assessed in cancer patients by using ultrasensitive immunocytochemical and molecular assays able to detect even single metastatic cells. To date, clinical studies with large study populations, validated immunoassays, and adequate follow-up time provide evidence for the independent prognostic value of the presence of disseminated tumor cells in the bone marrow. At present, bone marrow evaluation may therefore be considered a diagnostic tool for improved risk assessment with regard to distant relapse and death, especially among potentially curable breast cancer patients. Except for promising pilot studies, no data are available to support the immediate use of bone marrow evaluation for treatment monitoring in order to enable the prediction of response to adjuvant therapy.

Detection and prognostic value of cytokeratin positive tumor cells in bone marrow of patients with renal cell carcinoma

PURPOSE

Several investigations indicate the prognostic value of disseminated cytokeratin positive tumor cells in bone marrow of patients with carcinoma of different origin. In this study we evaluated the prognostic significance of epithelial cells in bone marrow of patients with renal cell carcinoma (RCC).

MATERIALS AND METHODS

Aspiration of bone marrow was performed preoperatively in 335 patients with RCC between 1990 and 1998. A total of 287 patients fulfilled all study inclusion (eg M0 R0 tumor stage) and exclusion (eg second malignancy during followup) criteria for the final analysis. Cytospin preparations were made after density gradient centrifugation of bone marrow samples and incubated with monoclonal antibodies directed against cytokeratin 18 (CK2) and pan-cytokeratin. Staining was performed using the alkaline phosphatase-anti-alkaline phosphatase method and 256 samples were evaluated. RESULTS In 25% (63 of 256) of the patients cytokeratin positive (CK+) cells were detected in bone marrow. Tumor progression (defined as tumor associated death, local recurrence or new metastases) was present in 12% (31 of 256) during the followup period (median 40 months), and 14% (9 of 63) with CK+ cells and 11% (22 of 193) with negative bone marrow status exhibited tumor progression. Survival analysis (log-rank test) showed no significant difference between the CK+ and cytokeratin negative group. The detection of CK+ cells was not an independent prognostic parameter in multivariate analysis (Cox regression model).

CONCLUSIONS

These results indicate that the immunocytochemical detection of disseminated cytokeratin positive tumor cells in the bone marrow of patients with RCC has no prognostic significance.

Disseminated tumor cells in bone marrow of patients with transitional cell carcinoma: immunocytochemical detection and correlation with established prognostic indicators

PURPOSE

Previous investigations have demonstrated the prognostic value of disseminated cytokeratin positive cells in bone marrow of patients with breast, gastric, colon and prostate cancer. We evaluated the potential of an immunocytochemical assay, using a monoclonal antibody against cytokeratin 18 (CK 18), for the detection of disseminated tumor cells in bone marrow aspirates of patients with transitional cell carcinoma.

MATERIALS AND METHODS

Bone marrow aspiration was performed preoperatively on 128 patients with transitional cell carcinoma of various stages and on 27 controls with nonmalignant disease. Cytospin preparations of mononuclear bone marrow cells were incubated with a monoclonal anti-CK 18 antibody and stained using the alkaline phosphatase anti-alkaline phosphatase technique.

RESULTS

Of the patients with transitional cell carcinoma 29.7% and none of the controls had a CK 18 positive bone marrow result. A significant correlation between the incidence of CK 18 positive cells in bone marrow and invasive transitional cell carcinoma (p <0.01), lymph node involvement (p <0.01), medium/high grade transitional cell carcinoma (p <0.01) and tumor progression in recurrent transitional cell carcinoma (p <0.05) was demonstrated. Furthermore, the mean number of CK 18 positive cells in bone marrow aspirates of patients with stage M+ and/or N+ disease was nearly 3 times as high as that of patients without clinically evident metastatic disease (10.4 versus 3.8 CK 18 positive cells per patient).

CONCLUSIONS

A significant correlation between the incidence of CK 18 positive bone marrow results in patients with transitional cell carcinoma and established risk factors could be demonstrated in our study. Further prospective followup studies should be performed to determine the prognostic value of these findings.

Minimal residual disease in gastric cancer: evidence of an independent prognostic relevance of urokinase receptor expression by disseminated tumor cells in the bone marrow

PURPOSE

To study the invasion-related molecule urokinase-type plasminogen activator receptor (u-PAR) expressed by disseminated tumor cells as a biologic predictor of poor survival in a large prospective series of patients with gastric cancer.

PATIENTS AND METHODS

In 156 gastric cancer patients (prospective series), disseminated tumor cells in the bone marrow and the u-PAR expressed by these tumor cells were determined by cytokeratin (CK) 18 immunocytochemistry and u-PAR/CK18 double immunocytochemistry.

RESULTS

In contrast to the mere detection of disseminated tumor cells at primary surgery, the additional evidence of u-PAR on these cells correlated significantly with pathologic T stage (P =.0474) and the expression of u-PAR (P =.0093) and plasminogen-activator inhibitor 1 (P =.0145) in the primary tumor (immunohistochemistry, chi(2)). Kaplan-Meier analysis revealed no association with prognosis for the mere detection of disseminated tumor cells. In contrast, a significant association was seen between detection of u-PAR on these cells and shorter disease-free (P <.0001) and overall survival (P <.0001). Multivariate analysis revealed that u-PAR on disseminated tumor cells at the time of primary surgery is an independent prognostic factor for disease-free (95% confidence interval [CI], 1.72 to 3.21; P =.024) and overall survival (P =.0049; relative risk, 2.89; 95% CI, 1.92 to 4.30).

CONCLUSION

This is the first large study to show that u-PAR, detected on disseminated tumor cells in the bone marrow, is an independent prognostic parameter in gastric cancer, in contrast to the mere detection of minimal residual disease (MRD). u-PAR may be a promising marker to define a critical subpopulation of disseminated tumor cells and a target to eliminate MRD. Molecular phenotyping of MRD is critical for defining its individual clinical relevance.

Molecular determinants of occult metastatic tumor cells in bone marrow

The success of mammographic screening for breast cancer is that it involves increasingly more patients with small primary tumors formerly thought to have an overall excellent prognosis. Yet, only approximately two thirds of these patients actually have this favorable prognosis, while the remaining third develops metastatic disease. Thus, there is emerging evidence that epithelial tumor cells can disseminate into secondary organs at an earlier stage of primary tumor development than appreciated by current risk classifications. Bone marrow is one of the most prominent secondary organs screened for the presence of disseminated tumor cells. The current data suggest that bone marrow micrometastases represent a selected population of dormant and heterogeneous cancer cells. The analysis of micrometastatic cells opens a new avenue by which to assess the molecular determinants of both early tumor cell dissemination and subsequent outgrowth into overt metastases. Moreover, identifying therapeutic target structures (e.g., HER2/neu), monitoring the elimination of bone marrow micrometastases, and assessing treatment-resistant tumor cell clones might help to understand the current limitations of adjuvant systemic therapy. This review summarizes the current knowledge of the biological characteristics of micrometastatic cancer cells in bone marrow of breast cancer patients.

MHC class I negative phenotype of disseminated tumor cells in bone marrow is associated with poor survival in R0M0 breast cancer patients

Changing the major histocompatibility complex (MHC) class I phenotype is a pivotal strategy of tumor cells to circumvent an effective immune response and is associated with tumor progression in cancer patients. Epithelial cells in bone marrow have been detected in various tumor types, but the clinical observation that only a portion of the patients with a positive bone marrow status develops solid bone metastasis suggests a certain molecular equipment of the isolated tumor cells as a prerequisite for metastatic formation. In the present study the prognostic impact of the MHC class I phenotype of disseminated epithelial cells in bone marrow was evaluated in a cohort of 30 curatively resected (R0) patients without distant metastases (M0) (designated R0M0) who had minimal residual disease. Immunocytochemical analysis using the alkaline/anti-alkaline immunogold double staining procedure revealed a heterogeneous MHC class I expression profile [monoclonal antibody (mAb) W6/32] of the epithelial cells (mAb CK2). In 16 patients (53.3%) all epithelial cells were human leukocyte antigen (HLA) class I-positive (CK2+//W6/32+ phenotype). Eight patients (26.7%) showed complete loss of the HLA class I molecules (CK2+//W6/32- phenotype) and in 6 patients (20%) partial loss of HLA class I expression was found (CK2+//W6/32+ and - phenotype). CK2+ cells with the HLA class I negative phenotype (CK2+//W6/32- phenotype and CK2+//W6/32+ and - phenotype) were often derived from poorly differentiated (G3) primary breast carcinomas (p = 0.036) and were associated with short survival of the R0M0 patients (follow-up 15-98 months, log rank p = 0.072). These findings support the necessity to develop immmunotherapeutic strategies leading to the restoration of MHC class I positive phenotype.

Disseminated cytokeratin positive tumor cells in the bone marrow of patients with prostate cancer: detection and prognostic value

PURPOSE

Previous investigations have shown that cytokeratin 18 positive bone marrow cells in localized and lymphatically spread prostate cancer correlates with neither established prognostic factors nor with the biochemical and clinical course after radical prostatectomy. Since the well-known down-regulation of cytokeratin 18 in tumor cells may lead to false-negative results, we asked whether staining with a pan-cytokeratin antibody recognizing a common epitope of cytokeratins 8, 18 and 19 would result in different data.

MATERIALS AND METHODS

Preoperative bone marrow aspirates of 82 patients with localized (N0) and lymphatically spread (N1) prostate cancer were examined using the monoclonal antibody cytokeratin 2 and the pan-cytokeratin antibody A 45-B/B3, called A 45.

RESULTS

In contrast to findings with the cytokeratin 18 antibody, those with the pan-cytokeratin antibody correlated with the biochemical course. At a median followup of 1,477 days (4 years) patients with pan-cytokeratin positive cells in the preoperative bone marrow aspirate had biochemical progression significantly earlier than those with pan-cytokeratin negative results (mean time to prostate specific antigen relapse 886 versus 1,409 days, p < or =0.004). Compared with other parameters, such as prostate specific antigen, pathological stage and Gleason score, preoperative pan-cytokeratin findings proved to be an independent prognostic factor.

CONCLUSIONS

Cytokeratin positive cells in the bone marrow also have prognostic relevance in prostate cancer. The comprehensive analysis of these cells, studies of the individual course of these findings and sufficiently long followup allow us to discuss whether and under what conditions metastasis may develop from 1 or several cytokeratin positive cells.

Lysis of prostate carcinoma cells by trifunctional bispecific antibodies (alpha EpCAM x alpha CD3)

Bispecific monoclonal antibodies (bsAbs) are a promising immunotherapeutic option for treatment of cancer, especially in situations of minimal residual disease. The combination of an anti-CD3 and anti-tumor-associated antigen antibody redirects cytotoxic T-lymphocytes towards malignant cells. Using a trifunctional bispecific antibody against EpCAM x CD3, that additionally activates Fc gamma R(+) accessory cells via its Fc region, we investigated the interaction between three EpCAM(+) prostate carcinoma cell lines and peripheral blood mononuclear cells (PBMCs) of healthy donors and patients with prostate carcinoma (PC). Visualization was performed by double immunocytochemical methods and computerized sequential video microscopy. Tumor cells and PBMCs supplemented with alpha EpCAM x alpha CD3 in 16-well chamber slides resulted in lysis of tumor cells within 1--3 days without any differences between patient and healthy donor PBMCs. The characteristic necrotic way of tumor cell killing (rounding, swelling, disrupting) could be observed in computerized sequences of video frames. Simultaneously, we could not reveal any form of apoptotic signal using three different apoptotic markers (TUNEL, M30 cyto death, anti-active caspase 3). Within the first 48 hr we observed typical PBMC cluster formation with increasing cell proliferation. PBMCs surrounding the tumor cells were not dominated by CD4(+), CD8(+), or CD14(+) cells. Lymphocytes with pore-forming perforin proteins concentrated towards the tumor target cells. Our combination of double immunocytochemical and computerized video microscopic techniques may serve as an important improvement of validity of cell-cell interaction experiments using in vitro models. (J Histochem Cytochem 49:911-917, 2001)

Orthotopic transplantation model of human gastrointestinal cancer and detection of micrometastases

AIM: To establish a relevant animal model of human gastrointestinal cancer, which can be used for repetitive investigations, so as to improve our understanding and management of carcinogenesis and cancer metastasis.

METHODS: Intact tissues of human colorectal and pancreatic cancers were transplanted in nude mice. The biological characteristics of the original and the corresponding transplanted tumors were investigated by HE staining, PAS staining and immunostaining. The metastases in the livers and lungs of nude mice were investigated by immunostaining with biotinylated mab KL-1 and by RT-PCR using CK20 specific primers.

RESULTS: There were totally 9 of 16 surgical specimens growing in nude mice subcutaneously and/or orthotopically (4 of 6 colorectal and 5 of 10 pancreatic cancer). Tumor cell content of the specimens and freezing of tissue specimens are important factors influencing the growth of transplanted tumor. In the group of fresh tumor tissues with greater than 50% tumor cell content, the success rate of the transplantation was 100% (3 cases of pancreatic cancer and 3 cases of colorectal cancer). The orthotopically transplanted tumors resemble the original tumor morphologically and biologically, including TAA expression such as CEA by immunohistochemistry, and CEA level in the serum of mice. Ki-67 labeling index and the expression of TAA especially K-ras, 17-1A and RA-96, are associated with the potential of tumor growth in nude mice. Micrometastases in the lungs and livers of tumor bearing mice can be detected by immunostaining with biotinylated mab KL-1 and CK20-specific RT-PCR.

CONCLUSION: An orthotopic transplantation model for human colon and pancreatic cancer in nude mice has been set up. We have also established sensitive detection methods with CK-immunohistochemistry and CK20-RT-PCR to study xenotransplanted human cancer and its metastatic cancer cells in the liver and lung of nude mice. This study may be helpful in understanding the mechanism of cancer metastasis and in developing new diagnostic methods and therapeutic strategies for metastases including micrometastases.

Characterization of disseminated tumor cells

The most prominent secondary organs screened for the presence of occult disseminated tumor cells are regional lymph nodes and bone marrow. The current data suggest that micrometastatic cells represent a selected population of dormant cancer cells, which still express a considerable degree of heterogeneity. The analysis of micrometastatic cells will open a new avenue to assess the molecular determinants of both early tumor cell dissemination and subsequent outgrowth into overt metastases. Moreover, identifying therapeutic target structures (e.g., HER2), monitoring the elimination of bone marrow micrometastases, and assessing treatment-resistant tumor cell clones may help in understanding the current limitations of adjuvant systemic therapy. This review summarizes the current knowledge on the biological characteristics of micrometastatic cancer cells in bone marrow and lymph nodes of cancer patients.

Implications of occult metastatic cells for systemic cancer treatment in patients with breast or gastrointestinal cancer

The early and clinically occult spread of viable tumour cells to the organism is becoming acknowledged as a hallmark in cancer progression, since abundant clinical and experimental data suggest that these cells are precursors of subsequent distant relapse. Using monoclonal antibodies against epithelial cytokeratins or tumour-associated cell membrane glycoproteins, individual carcinoma cells can be detected in cytological bone marrow preparations at frequencies of 10(-5) to 10(-6). Prospective clinical studies have shown that the presence of such immunostained cells in bone marrow is prognostically relevant with regard to relapse-free and overall survival, even in malignancies that do not preferentially metastasise to bone. As current treatment strategies have resulted in a substantial improvement of cancer mortality rates, it is noteworthy to consider the intriguing options of immunocytochemical screening of bone marrow aspirates for occult metastatic cells. Besides improved tumour staging, such screening offers opportunities for guiding patient stratification for adjuvant therapy trials, monitoring response to adjuvant therapies (which, at present, can only be assessed retrospectively after an extended period of clinical follow-up), and specifically targeting tumour-biological therapies against disseminated tumour cells. The present review summarises the current data on the clinical significance of occult metastatic cancer cells in bone marrow.

Bone marrow micrometastases and gastrointestinal cancer detection and significance

Accurate staging of cancer is important, as the presence or absence of systemic spread determines treatment. The sensitivity of current imaging and biochemical techniques is suboptimal for the detection of minimal residual disease and latent metastases. This results in understaging and potential undertreatment. To improve detection of disseminated epithelial malignancy, immunohistochemical and molecular methods have been employed that search for epithelial cell-specific proteins in nonepithelial tissue. Bone marrow is mesenchymal tissue (that does not normally express epithelial cell components) and represents an accessible window for detection of micrometastatic carcinoma cells. Detection methods for epithelial cell components (cytokeratins, epithelial membrane antigen, carcinoembryonic antigen) include immunohistochemistry, flow cytometry, reverse transcriptase polymerase chain reaction (rt-PCR), and enzyme linked immunoassay (ELISA). Micrometastatic cells in bone marrow are viable, capable of proliferation, resistant to immune attack, and insensitive to s-phase chemotherapeutic agents. Patients with carcinomas of the lung, breast, prostate, or gastrointestinal tract and in whom bone marrow micrometastases are detected have a foreshortened interval to recurrence and impaired survival. Detection of micrometastases deserves serious consideration in treatment protocols, and standardization of methods is now required.

Detection of extraprostatic prostate cells utilizing reverse transcription-polymerase chain reaction

This article reviews the utility of reverse transcription-polymerase chain reaction (RT-PCR) in prostate cancer. RT-PCR aims to detect occult micrometastases in non-prostatic sites. Due to its exquisite analytical sensitivity, RT-PCR is able to amplify and detect even low-level, prostate-specific messages present at these extraprostatic sites. In recent years, a fair amount of data on the clinical utility of the technique had been reported. The target tissues under investigation are peripheral blood, bone marrow aspirate, and lymph nodes. Favorite markers of choice are prostate-specific antigen (PSA), prostate-specific membrane antigen (PSMA), and human glandular kallikrein-2 (hK2). False positives among negative controls are low. For the most part, RT-PCR is inadequate in detecting tumor cells in the peripheral blood from patients who are known to have metastatic prostate cancer. All studies showed that RT-PCR could detect PSA, PSMA or hK2 mRNAs in the circulation of patients who have organ-confined or extraprostatic disease. Most studies showed that RT-PCR utilizing current markers could not be used as a prospective test to diagnose prostate cancer. However, a few studies also showed that the detection rate could be predictive and sensitive enough to differentiate patients with organ-confined disease from those with extraprostatic disease. Data from PSA- or PSMA-RT-PCR using lymph nodes as the tissue source is more encouraging. RT-PCR was able to detect PSA and/or PSMA positive samples that have not been detected by conventional pathology.

Micrometastases of bone marrow in localized prostate cancer: correlation with established risk factors

PURPOSE

The presence of cytokeratin 18-positive cells in bone marrow correlates with conventional risk factors in many tumors. We examined whether this was also valid for localized or lymphatically spread prostate cancer.

PATIENTS AND METHODS

Immediately before radical prostatectomy, bone marrow aspirates from both sides of the iliac crest were taken from 287 patients. The presence of cells containing cytokeratin 18 was interpreted as micrometastasis.

RESULTS

In patients with negative lymph nodes (n = 219), conventional risk factors (Gleason score, pathologic stage, ploidy, and preoperative prostate-specific antigen) did not correlate with the preoperative detection of cells containing cytokeratin 18. There was also no correlation with lymph node metastases. Furthermore, there was no interdependency between the preoperatively detected number of cells and the established risk factors.

CONCLUSION

We assume the presence of epithelial cells in bone marrow to be an independent parameter, the clinical importance of which must be substantiated by further studies.

Immunocytological detection of isolated tumour cells in the bone marrow of malignant melanoma patients: a new method for the detection of minimal residual disease

AIMS

Immunocytologically detected isolated tumour cells indicate a poor prognosis. This has been shown in breast, gastrointestinal and lung cancer, and might thereby help to indicate adjuvant therapy. Immunocytology has been proved to be a reliable technique and enables a phenotypic tumour cell characterization. We find this technique superior to molecular biological techniques such as reverse transcriptase polymerase chain reaction RT-PCR. So far, immunocytological studies have not been performed in malignant melanoma patients and our study aimed to establish this approach in melanoma patients.

METHODS

Twenty melanoma patients who underwent surgery for lymph-node metastasis using a radical lymphadenectomy were studied. Using the immunoperoxidase method, cytospins of bone marrow aspirates (1.5x10(6)cells per patient) were stained with the monoclonal antibody HMB-45. Nineteen patients who were surgically treated but did not suffer from malignant melanoma were included as a control group.

RESULTS

Four of the 20 patients showed isolated tumour cells in the aspirate. Three of these patients had stage IV disease. One patient had a stage III tumour (1/7; 14.3%). One patient was classified as stage II and did not show tumour cells in the bone marrow. No staining cells were found in the control group (n=19).

CONCLUSIONS

Our study demonstrates that the immunocytological approach can be used as a new technique to detect occult tumour cell dissemination in malignant melanoma patients and supports previous findings in carcinoma of the stomach, colon, pancreas and other tumours.

Micrometastatic bone marrow involvement: detection and prognostic significance

The present review focuses on the methodology and clinical significance of new diagnostic approaches to identify individual cancer cells present in bone marrow, both as a frequent site of metastasis formation and an indicator organ for hematogenous tumor cell dissemination. The steadily increasing number of studies on this issue is characterized by considerable methodological variations of important variables, such as the size of the study population, and the reliability of monoclonal antibodies used for tumor cell detection. Emerging data indicate that this disturbing heterogeneity might be overcome by the use of reliable and specific anti-cytokeratin antibodies (for example, A45-B/B3) as, for the time, standard markers for the detection of micrometastatic tumor cells in bone marrow. Prospective clinical studies have shown that immunoassays based on anti-CK antibodies identify patients' subgroups with a poor clinical prognosis with regard to early metastasis manifestation and reduced overall survival in various epithelial tumor entities, including breast, colon, rectum, stomach, esophagus, prostate, renal, bladder, and non-small cell lung cancer. The immunocytochemical assays may be therefore used to improve tumor staging with potential consequences for adjuvant therapy, because disseminated cells appeared to be dormant, non-cycling (for example Ki-67 antigen-negative) cells, suggesting a resistance to cell-cycle dependent therapy, such as chemotherapy. Therefore, cell-cycle independent antibody-based immunotherapy might be an interesting option to complement chemotherapy. Another promising clinical application is monitoring the response of micrometastatic cells to adjuvant therapies, which, at present, can only be assessed retrospectively after an extended period of clinical follow-up. The outlined current strategies for detection and characterization of cancer micrometastasis might help to design and control new therapeutic strategies for secondary prevention of metastatic relapse in patients with operable primary carcinomas.

Immunoglobulin and enzyme-conjugated dextran polymers enhance u-PAR staining intensity of carcinoma cells in peripheral blood smears

The presence of disseminated carcinoma cells in bone marrow and peripheral blood has prognostic importance in patients with carcinomas. Much evidence indicates that dissemination of tumor cells may depend on activation of a variety of degradative enzymes. A strong positive correlation has been shown between the expression of tumor cell proteases and tumor invasion. Therefore, phenotypic characterization of disseminated carcinoma cells for expression of protease activators might define the invasive potential of the cells. We present an immunocytochemically enhanced staining method that allows phenotyping of disseminated carcinoma cells in bone marrow and peripheral blood smears. In the first step, the cells were incubated with antibodies against urokinase plasminogen activator receptor (u-PAR) and subsequently with secondary antibodies conjugated to peroxidase-labeled dextran polymers. A brown color reaction was developed with diaminobenzidine as chromogen. In the second step, the cells were incubated with alkaline phosphatase-conjugated murine monoclonal antibodies against a common cytokeratin epitope and a red color reaction was developed with new fuchsin as substrate. This method allows simultaneous and unambiguous immunolabeling of intracellular cytokeratin and of u-PAR intracellularly and on the surface of carcinoma cells. This novel approach can be used for detection and phenotyping of carcinoma cells in blood smears for u-PAR or, presumably, for any other heterogeneously expressed antigen on the surface of the detected cells.

Comparative immunocytochemical assessment of isolated carcinoma cells in lymph nodes and bone marrow of patients with clinically localized prostate cancer

After radical prostatectomy for clinically localized prostate cancer, biochemical progression is seen in up to 40% of the patients due to persistent local and/or systemic remnants. Isolated disseminated carcinoma cells, undetectable by current staging methods, are of special interest as potential precursors of subsequent overt metastases. In the present study, immunohistochemistry (IHC) was performed to evaluate simultaneously the frequency of occult carcinoma cells in both lymph nodes (LNs) and bone marrow (BM) obtained from the iliac crests of 45 prostate cancer patients with untreated stage T(1-3) pN0 M0 prostatic carcinoma. IHC using monoclonal antibodies (MAbs) against epithelial cytokeratins was performed on 521 paraffin-embedded LNs histopathologically classified as tumorfree (pN0), as well as on BM cytospin preparations. To confirm the prostatic origin of positive cells in LNs, additional IHCs for prostate-specific antigen (PSA) and epithelial glycoproteins were performed. In total, isolated tumor cells in LNs and/or BM were detected in 17 of the 45 patients. Parameters such as tumor stage, grade and volume of the primary tumor as well as blood serum PSA levels could not detect patients harboring disseminated single tumor cells in LNs or BM. Following a median observation time of 24.9 months, no significant correlation between IHC positivity and PSA progression as a measure of early relapse was observed. Although the overall incidence of occult tumor cell spread corresponds to similar incidence of relapses after radical prostatectomy as reported by others, the fate of these cells needs to be evaluated in longer follow-up studies.

Tumor-antigen heterogeneity of disseminated breast cancer cells: implications for immunotherapy of minimal residual disease

Single micrometastatic tumor cells encased in mesenchymal tissues, such as bone marrow (BM), are regarded as suitable targets for adjuvant immunotherapy since they are easily accessible for both immunoglobulins and immune effector cells. However, the antigen profile of such cells, to which antibody therapy might be targeted, cannot be deduced from the antigen pattern of the primary tumor. To evaluate the antigen profile of disseminated cells found in BM aspirates from 20 breast cancer patients, we applied a quantitative immuno-cytochemical double-marker assay and typed for 4 common tumor-associated cell-surface antigens (c-erbB-2, CO17-1A, MUC-1, LewisY). Individual breast cancer cells were identified by F(ab) fragments of the pan-cytokeratin (CK) monoclonal antibody (MAb) A45-B/B3, directly conjugated with alkaline phosphatase, which identified cancer cells as sensitively as the standard APAAP procedure (r = 0.998; p < 0.0001). CK+ cells co-expressed c-erbB-2, CO17-1A, MUC-1 and LewisY in 87%, 78%, 79% and 79% of patients, respectively; however, the frequency of double-positive cells per sample varied considerably. The mean percentage of double-positive cells per total number of CK+ cells was 41% for c-erbB-2 (range 0-92%), 47% for CO17-1A (range 0-75%), 49% for MUC-1 (range 0-67%) and 32% for LewisY (range 0-59%). In 14 of these patients, we used an antibody cocktail to type CK+ cells for the combined expression of all 4 antigens. The antibody cocktail labeled significantly more CK+ cells than each of the single MAbs alone, resulting in a mean of 71% double-positive tumor cells (34-100%). We conclude that expression of tumor-associated cell-surface antigens on micrometastatic cancer cells in BM is heterogeneous, which may limit the efficacy of monovalent immunotherapeutic strategies directed against only one particular antigen. Thus, defining target antigens expressed by the actual target cells emerges as a crucial first step in selecting appropriate therapeutic targets.

Selection of potentially metastatic subpopulations expressing c-erbB-2 from breast cancer tissue by use of an extravasation model

Overexpression of the crbB-2 gene-encoded p185(c-erbB-2) is correlated with early onset of metastasis in breast cancer patients. Furthermore, the detection of blood-borne epithelium-derived clustered cells expressing p185(c-erbB-2) was related to advanced stages in breast cancer. To further elucidate the receptor's function in the metastatic process of human breast cancers, we analyzed disaggregated cells and cell clusters from freshly dissected breast cancer tissues. We studied whether their capability of extravasation is correlated with their expression of c-erbB-2. A model for the venular wall was constructed by growing human umbilical vein endothelial cells (HUVECs) on porous membranes coated with basement membrane extracellular matrix. In four control breast cancer cell lines (SK-BR-3, MCF-7, MDA-MB-468, and MDA-MB-468, the latter transfected with a full-length c-erbB-2 cDNA vector) producing different levels of the c-erbB-2 receptor, the expression level correlated positively with the invasiveness of the cells. The invasive, predominantly clustered cells from 14 of 23 tumors were positively stained for p185(c-erbB-2) by immunocytochemistry. Furthermore, we show that the invasive cell populations express the metastasis-associated proteins matrix metalloproteinase MMP-2, CD44, and integrins alpha(v)beta3 and alpha6. In this first study on the behavior of cells and cell clusters from disaggregated operated cancers in an extravasation model, we could demonstrate the presence of c-erbB-2-expressing cell subpopulations within the individual breast cancers that are presumably of high metastatic potential.

Simultaneous detection of two independent antigens by double staining with two mouse monoclonal antibodies

Simultaneous detection of two antigens by immunostaining usually requires primary antibodies from two different species or a hapten modification of one of the antibodies if they are from the same species. A novel double staining method is described for immunodetection of two independent antigens using two mouse monoclonal antibodies. The principle of the method is the following: The first antigen is detected by a monoclonal antibody that is diluted so extensively that it cannot be recognized with conventional detection systems. A highly sensitive biotin-tyramide amplification system is used to identify this antibody. The second antigen is stained with a monoclonal antibody by dilution and detected by conventional immunostaining. The method was tested for both alkaline-phosphatase staining on paraffin sections and immunofluorescence staining on cultured cells in cytospin preparation. The absence of cross-reaction in the former system was demonstrated by the mutually exclusive detection of T- and B-cells in human lymph nodes or T-cells and carcinoma cells in nasopharyngeal carcinoma biopsies. Similarly, the EBV encoded EBNA2 and ZEBRA proteins showed a mutually exclusive staining by immunofluorescence on B95-8 cells. The method could be used to demonstrate co-expression of two independent antigens in the same cells, such as PCNA and keratin in carcinoma cells in paraffin sections and for EBNA2 and LMP1 EBV proteins in immunofluorescence preparations of B95-8 cells.

Isolation of blood-borne epithelium-derived c-erbB-2 oncoprotein-positive clustered cells from the peripheral blood of breast cancer patients

Clinical studies including thousands of breast cancer patients have shown that c-erbB-2 is amplified and overexpressed in 20-30% of invasive human breast cancers and that it is associated with distant metastasis in specified patient subgroups. To isolate and characterize hematogeneously spreading c-erbB-2-positive epithelium-derived cells from the peripheral blood of breast cancer patients, a combined buoyant density gradient and immuno-magnetic separation method has been used. The method utilizes a biotinylated anti-cytokeratin monoclonal antibody (MAb) for capturing the epithelium-derived cells. The expression of c-erbB-2 by the captured cells was detected using an anti-c-erbB-2 rabbit antibody (21N) coupled to an anti-rabbit gold-labeled anti-body, whereby immunoenzymatic cytokeratin staining was performed using a silver-enhanced immunogold double staining protocol. In total, 29 of the 46 patients tested had either cytokeratin (24/29) or cytokeratin/c-erbB-2 (19/29) positive clustered cells in their peripheral blood. We thus report here the presence and the frequency of clone-specifically stained clustered cells in the peripheral blood of breast cancer patients. The frequency of cytokeratin/c-erbB2 double-positive clustered cells in the peripheral blood was on average 10 times higher than that of double-positive single cells. The numbers of cytokeratin/c-erbB-2 double-positive clustered cells were positively correlated with the stage of tumors. Results of in vitro motility experiments using single and clustered cells from primary breast cancer tissue strongly support the assumption that cytokeratin/c-erbB-2 double-positive clustered cells have a high potential for locomotion. We suggest that blood-borne epithelium-derived c-erbB-2-positive clustered cells are the possible precursor cells responsible for the formation of distant metastases and bone marrow micrometastases.

Prognostic relevance of cathepsin D detection in micrometastatic cells in the bone marrow of patients with primary breast cancer

Patients with an elevated level of cathepsin D in breast cancer tissue have an adverse prognosis. This study evaluated the prognostic relevance of cathepsin D detection in disseminated tumour cells in bone marrow. Bone marrow was sampled intraoperatively from both anterior iliac crests in 290 patients with primary breast cancer. Interphase cells were enhanced and stained immunocytologically with two antibodies: BM2, which detects tumour-associated glycoprotein TAG 12, which is typically expressed by almost all breast cancer cells, and the anti-cathepsin D antibody. 67 of 149 BM2-positive women (45%) developed metastatic disease (median follow-up time: 69 months). Of these, 15 were cathepsin D-positive (22%). Patients with cathepsin D-positive cells in bone marrow (n = 26; 9%) had a significantly shorter metastasis-free interval (38 months) compared with women who were cathepsin D-negative (64.5 months). The worst prognosis was seen in patients positive for both markers (30.5 months), followed by those who were cathepsin D-negative and BM2-positive (48 months). The detection of cathepsin D on disseminated tumour cells characterises a subgroup of patients with a poorer prognosis who should undergo more aggressive adjuvant systemic therapy.

Isolated tumor cells are frequently detectable in the peritoneal cavity of gastric and colorectal cancer patients and serve as a new prognostic marker

OBJECTIVE

To evaluate the prognostic significance of isolated tumor cells detected by a panel of various monoclonal antibodies.

SUMMARY BACKGROUND DATA

Previously, we showed by using immunocytology that cancer cells are frequently found in bone marrow and peritoneal cavity samples of gastrointestinal cancer patients.

METHODS

Findings in bone marrow and peritoneal cavity samples were compared and correlated with the 4-year survival rate of 84 gastric and 109 colorectal patients with cancer.

RESULTS

Although positive results in the bone marrow showed little prognostic significance, the peritoneal cavity results correlated with the 4-year survival rate (gastric cancer: p = 0.0038; colorectal cancer: p = 0.0079). Additionally, in subgroups of patients with early (gastric cancer: p = 0.02, colorectal cancer: p = 0.48) and advanced (gastric cancer: p = 0.02, colorectal cancer: p < 0.0001) tumor stages, a correlation of immunocytologic findings and the survival rate was seen.

CONCLUSIONS

The detection of minimal residual disease in the peritoneal cavity serves as a new prognostic marker.

Prognostic factors in gastric cancer

BACKGROUND

Despite gastric cancer being common, its prognosis has not been improved significantly in recent years. Now, greater insight has been gained into the biological properties of tumour cells, how they become malignant and what mechanisms they may use to invade and metastasize. This involves tumour-associated protease systems, loss or mutation of adhesion molecules and changes in genetics. The view of gastric cancer is changing: it is not only a solid tumour but also exhibits a minimal residual disease component even in the early stages of disease. Such biological tumour characteristics may provide new prognostic factors and also potential new therapeutic options.

METHODS

This is an update of prognostic factors in gastric cancer, emphasizing new biological features, some of which have been investigated by this group over the past few years. Current results are discussed in the light of 212 references obtained from the Medline database from 1979 to 1997.

RESULTS

There is high probability that some of the factors reviewed, such as c-erbB-2, individual course and phenotyping of disseminated tumour cells will become significant new prognostic variables. This is true also, to a lesser extent, of cathepsin D, matrix metalloproteinase 2 combined with activators or tissue inhibitor of metalloproteinases 2, CD44, E-cadherin, p53 and cripto. Plasminogen activator inhibitor 1 (PAI-1), a member of the urokinase-type plasminogen activator (uPA) system, can already be defined as an established new prognostic factor in gastric cancer.

CONCLUSION

PAI-1 should be considered prognostically in addition to established tumour classifications. Moreover, the uPA system is a target for future therapeutic concepts. Further analysis of factors describing tumour biology should lead to new, functionally orientated, tumour classifications in gastric cancer.

Immunocytochemical monitoring of micrometastatic disease: reduction of prostate cancer cells in bone marrow by androgen deprivation

Occult dissemination of tumor cells mainly determines the prognosis of patients with primary prostate cancer. The effect of androgen deprivation on micrometastatic tumor cells in these patients is currently unknown. We therefore used an immunocytochemical assay with monoclonal antibodies (MAbs) directed against epithelial cytoskeleton proteins (i.e., cytokeratins) to monitor the concentration of isolated tumor cells in the bone marrow of 36 prostate cancer patients (stage C), who underwent hormonal androgen deprivation with Flutamide and Leuprorelin acetate. Tumor cells in cytologic bone marrow preparations were detected using an assay that employed the MAb CK2 directed against cytokeratin (CK) 18 and the alkaline anti-alkaline phosphatase staining method. Prior to therapy, we detected between 1 and 38 CK-positive cells per sample of 2 x 10(6) nucleated cells in 21 patients, while the remaining 15 patients displayed tumor-free marrow samples. There was no significant correlation between the concentration of CK-positive cells and the volume of hypo-echogenic lesions as an indicator of the primary tumor volume or the serum level of prostate-specific antigen (PSA). After androgen deprivation, 20 of the 21 initially positive patients either became negative (n = 16) or showed at least a reduction in the concentration of CK-positive cells (n = 4). Moreover, only 2 of the 15 patients with negative pre-treatment findings became positive. All of the 7 patients with remaining tumor cells in the bone marrow after therapy showed no detectable amounts of PSA in their serum. Our findings suggest that serum PSA concentration is no indicator of micrometastatic disease in bone marrow. Neoadjuvant androgen deprivation appears to eliminate disseminated CK-positive tumor cells present in bone marrow, a preferred site of overt metastasis in prostate cancer patients.

Immunocytochemical phenotyping of disseminated tumor cells in bone marrow by uPA receptor and CK18: investigation of sensitivity and specificity of an immunogold/alkaline phosphatase double staining protocol

Phenotyping of cytokeratin (CK)18-positive cells in bone marrow is gaining increasing importance for future prognostic screening of carcinoma patients. Urokinase-type plasminogen activator receptor (uPA-R) is one example of a potential aggressive marker for those cells. However, a valid and reliable double staining method is needed. Using monoclonal antibodies against uPA-R and CK18, we modified an immunogold/alkaline phosphatase double staining protocol. UPA-R/CK18-positive tumor cell controls exhibited black uPA-R staining in 15-80% of cases and red CK18 staining in almost 100% of tumor cells. Isotype- and cross-matched controls were completely negative. Bone marrow from healthy donors was always CK18-negative. Reproducibility of CK18-positive cell detection was estimated in a series of specimens from 61 gastric cancer patients comparatively stained with the single alkaline phosphatase-anti-alkaline phosphatase (APAAP) and our double staining method (10(6) bone marrow cells/patient). In four cases, double staining could not reproduce CK18-positive cells. In 34 cases it revealed fewer or equal numbers, and in 23 cases more CK18-positive cells than the APAAP method. Overall quantitative analysis of detected cell numbers (838 in APAAP, range 1-280 in 10(6); double staining 808, range 0-253) demonstrated relative reproducibility of APAAP results by double staining of 97%. Correlation of results between both methods was significant (p < 0.001, linear regression). Sensitivity of double staining tested in logarithmic tumor cell dilutions was one CK18-positive cell in 300,000. Specific uPA-R staining was seen on CK18-positive cells in bone marrow from 29 of 61 patients, and also on single surrounding bone marrow cells. To test the specificity of this staining, bone marrow cytospins from 10 patients without tumor disease were stained for uPA-R with the APAAP method. uPA-R expression was confirmed in all 10 cases, with a mean of 6.5% uPA-R-positive cells in 1000 bone marrow cells (SEM 1.2%). These results suggest that our double staining protocol is a sensitive, reproducible, and specific method for routine uPA-R phenotyping of disseminated CK18-positive cells in bone marrow of carcinoma patients.

Prognostic relevance of urokinase plasminogen activator detection in micrometastatic cells in the bone marrow of patients with primary breast cancer

Patients with an elevated level of urokinase plasminogen activator (uPA) in breast cancer tissue have an adverse prognosis. This study evaluated the prognostic relevance of uPA detection in disseminated tumour cells in bone marrow. Bone marrow was sampled intraoperatively from both iliac crests in 280 patients with primary breast cancer. Interphase cells were enhanced and stained immunocytologically with two antibodies: 2E11, which detects TAG 12--a tumour-associated glycoprotein typically expressed by almost all breast cancer cells--and the anti-uPA antibody HD-UK9. Thirty-five of the 2E11-positive women (n = 132, 47%) developed metastatic disease (median follow-up time 44 months). Of these, most were uPA positive (n = 23, 65%) and only 12 were uPA negative. Patients with uPA-positive cells in bone marrow (n = 98, 35%) had a significantly shorter metastasis-free interval (36 months) than women who were uPA negative (44.5 months). The worst prognosis was seen in patients positive for both markers (29.5 months), followed by those who were uPA negative and 2E11 positive (37 months). The detection of uPA on disseminated tumour cells characterizes a subgroup of patients with an even worse prognosis, who should undergo more aggressive adjuvant systemic therapy. For the first time, it was possible to evaluate an important qualitative parameter involved in the process of breast cancer metastases.

Detection of minimal disease in patients with solid tumors

The detection and elimination of minimal systemic disease in patients with solid tumors is one of the main current topics in clinical oncology. The present review focuses, therefore, on new diagnostic approaches to identify minimal disease in peripheral blood, bone marrow, and lymph nodes of patients with epithelial cancer as the major type of solid tumors in Western industrialized countries. These approaches may be used to improve tumor staging and monitoring of adjuvant therapies, as well as to detect tumor cell contamination in autologous stem cell grafts. Most investigators have developed either immunocytochemical assays with monoclonal antibodies to a variety of epithelial-specific cytoskeleton and membrane antigens or molecular methods based on the extensive amplification of a specific (c)DNA sequence by the polymerase-chain reaction (PCR). In immunocytochemical assays, antibodies to cytokeratins can be regarded as the most specific and sensitive probes to detect isolated epithelial tumor cells in bone marrow and blood. Molecular methods are based on the detection of either mutations in oncogenes and tumor suppressor genes (e.g., ki-ras and p53 genes) or the mRNA expression of tissue-specific and tumor-associated genes. mRNA species targeted in these assays encode cytokeratins, prostate-specific antigen, prostate-specific membrane antigen, carcinoembryonic antigen, and polymorphic-epithelial mucin. To introduce the available methods into clinical practice, standardized protocols need to be developed and validated in multi-center studies.

Individual development and uPA-receptor expression of disseminated tumour cells in bone marrow: a reference to early systemic disease in solid cancer

It is unclear whether disseminated tumour cells detected in bone marrow in early stages of solid cancers indicate a subclinical systemic disease component determining the patient's fate or simply represent mainly irrelevant shed cells. Moreover, characteristics differentiating high and low metastatic potential of disseminated tumour cells are not defined. We performed repeated serial bone marrow biopsies during follow-up in operated gastric cancer patients. Most patients with later tumour relapse revealed either an increase or a constantly high number of tumour cells. In contrast, in patients without recurrence, either clearance of tumour cells or negative or low cell counts were seen. Urokinase plasminogen activator (uPA)-receptor expression on disseminated tumour cells was significantly correlated with increasing tumour cell counts and clinical prognosis. These results demonstrate a systemic component in early solid cancer, indicated by early systemically disseminated tumour cells, which may predict individual disease development.