Detection of melanoma cells in peripheral blood by means of reverse transcriptase and polymerase chain reaction

Detection of early micrometastases in subcutaneous fat of primary malignant melanoma patients by identification of tyrosinase-mRNA

To improve survival following melanoma excision, wide margin resection including subcutaneous fat, is indicated. Subcutaneous fat, resected with primary melanomas, was investigated using the tyrosinase PCR method originally described for detection of melanoma cells in peripheral blood. Identification of tyrosinase transcripts was possible in 4 melanoma patients (3 Clark level IV, 1 level III), while negative results were obtained from 6 other patients (2 level IV, 3 level III and 1 level I). In control experiments, after infiltration of the reference cell line SkMel into normal fat tissue, the PCR was positive in 33% (3/9) with 10(2) infiltrated cells, 69% (9/13) with 10(4) cells and in 100% (7/7) with 10(6) cells. We conclude that detection of melanoma cells in subcutaneous fat tissue is possible by tyrosinase PCR. Follow-up studies should show whether such positive tyrosinase PCR can define patients at very high risk of tumour relapse.

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.

Sensitive detection of circulating breast cancer cells by reverse-transcriptase polymerase chain reaction of maspin gene

BACKGROUND

Maspin, a recently identified protein related to the family of serpins, is believed to play a role in human breast cancer. In an effort to improve the present methods of detection, we have developed a reverse-transcriptase polymerase chain reaction (RT-PCR) assay for maspin transcript to identify small numbers of mammary carcinoma cells in the peripheral blood and bone marrow of patients with breast cancer.

PATIENTS AND METHODS

Five non-neoplastic mammary tissue samples, 13 breast cancer specimens as well as 17 peripheral blood and 4 bone marrow samples from normal subjects were screened for the presence of maspin mRNA by RT-PCR. The same assay was applied to peripheral blood or bone marrow samples obtained from 29 patients with stages I to IV breast cancer.

RESULTS

By RT-PCR it was possible to amplify maspin mRNA in all of the primary and metastatic breast cancer specimens, but in none of the normal hemopoietic samples from healthy donors. Thus, detection of maspin transcript in the peripheral blood or marrow of a patient known to have breast cancer is indicative of the presence of mammary carcinoma cells. In reconstitution experiments, maspin RT-PCR reliably detected 10 mammary carcinoma cells in 1 million normal peripheral-blood mononuclear cells (PBMCs). None of the 9 patients with stages I, II, or III breast cancer had maspin transcript in peripheral blood. Of note, 3 of 9 patients with stage IV breast cancer receiving systemic therapy at the time of sample collection, but only 1 of 11 patients with stage IV not receiving therapy, had detectable maspin transcript in peripheral blood. Moreover, 3 marrow specimens from stage IV patients tested positive by this assay.

CONCLUSIONS

This pilot study suggests that maspin RT-PCR assay is a sensitive, specific and sufficiently rapid method for detection of small numbers of circulating cells and marrow micrometastases in breast cancer patients. The possibility of applying this assay in the detection of tumor cell contamination of both marrow and stem-cell apheresis harvests of breast cancer patients merits further investigation.

Detection of ras gene mutations in perioperative peripheral blood with pancreatic adenocarcinoma

Surgeons wish to know of any correlation between an operation and the incidence of metastasis. In perioperative periods, pancreatic cancer cells were identified by detecting mutant K-ras gene by two-step PCR and RFLP analysis in blood samples taken from peripheral blood. In no case was K-ras point mutation detected in blood before operation, although the mutant hand was observed in all cases at the time the lesion was resected. Surprisingly, in five of ten cases, positive bands were identified just after laparotomy, before we had reached the primary lesion. In almost all cases, mutant K-ras was detected until the fourteenth postoperative day. These findings suggest that cancer cells exist in the circulation, and have a potential for hematogenous metastasis during the perioperative period. In conclusion, surgical stress causes hematogenous dissemination of pancreatic cancer cells, and surgeons should employ the appropriate anti-metastasis therapy in the perioperative period.

Metastatic potential of human melanoma cells in nude mice--characterisation of phenotype, cytokine secretion and tumour-associated antigens

Incidence and mortality of human malignant melanoma has risen rapidly over recent decades. Although the notorious resistance to treatment is characteristic for metastatic malignant melanoma, only a few experimental models have been established to study the metastatic cascade or to test new alternative treatment modalities. Thus, new human models are wanted. Here, we describe the metastatic behaviour of seven human melanoma cell lines derived from two primary cutaneous melanomas (WM 98-1, WM 1341) and five metastases established from liver (UKRV-Mel-4), skin (M7, M13), pleural effusion (UKRV-Mel-2) and lymph node (MV3). All cell lines were analysed for their capacity to grow in nude mice after s.c. and i.v. administration. M13 cells developed liver metastases spontaneously after s.c. injection, and subsequent passages of M13 and M7 melanoma cells caused liver metastases after i.v. injection, whereas MV3 and WM98-1 gave rise to lung metastases, using the same inoculation route. In contrast, WM 1341, UKRV-Mel-2 and UKRV-Mel-4 grew only very slowly in nude mice after s.c. injection and did not cause any metastases after i.v. or s.c. administration. The pattern of metastases or growth kinetics did not correlate with the interleukin 8 or tumour necrosis factor secretion of cell lines. Adhesion molecules and growth factor receptor expression on the cell lines differed widely, as determined by flow cytometry, with the low metastatic cell lines (UKRV-Mel-2, UKRV-Mel-4 and WM 1341) demonstrating a marked reduction in VLA-1 and VLA-5 expression compared with the metastatic lines (M7, M13, MV3 and WM 98-1). Expression of pigment-related proteins such as tyrosinase, TRP-1, TRP-2, Melan-A/MART-1, gp100, MAGE1 or MAGE-3 was not associated with growth and metastatic characteristics of the melanoma cell lines analysed. In conclusion, the established human melanoma cell lines exhibited diverse growth behaviour in nude mice in congruence with some early established prognostic markers such as VLA-1 and VLA-5. The xenografts provide good models for further study of metastatic processes as well as for evaluation of alternative treatment modalities including new pharmaceutical drugs and gene therapeutic targeting using tissue-specific gene regulatory elements for gene targeting.

Polymerase chain reaction in the detection of micrometastases and circulating tumor cells

BACKGROUND

The sensitive detection of circulating tumor cells and micrometastases may have important therapeutic and prognostic implications.

METHODS

The molecular detection of occult tumor cells can be accomplished by amplifying tumor specific abnormalities present in the DNA or mRNA of malignant cells with the polymerase chain reaction (PCR). This approach has been used mainly for hemato-lymphoid malignancies. The other main PCR strategy for the detection of minimal residual disease (MRD) involves amplification of tissue-specific mRNA. This method was applied for the detection of occult disease in solid tumors.

RESULTS

PCR was shown to be superior to conventional techniques in detecting circulating tumor cells and micrometastases allowing the identification of 1 tumor cell diluted with 10(6)-10(7) normal cells. The central question of whether PCR positivity reliably predicts relapse remains unanswered for many tumor types. Serial analysis of a large number of samples is needed and currently undertaken in many institutions.

CONCLUSIONS

PCR is a highly sensitive method for the detection of circulating tumor cells and micrometastases in solid and hematopoietic malignancies. If PCR positivity is found to be a reliable tool, this will likely have a major impact on the treatment of many cancers. Patients could be selected for systemic therapy at an earlier stage when the metastatic tumor burden is low. PCR may improve the preoperative staging of patients with epithelial malignancies and therefore help avoid unnecessary radical procedures. Furthermore, this test may be useful in monitoring the effectiveness of adjuvant therapy, the intensity and duration of which is tailored to the individual patient. The impact of this PCR based approach on clinical oncology is likely to be profound.

Sequential detection of tumor cells in the peripheral blood and bone marrow of patients with stage IV neuroblastoma by the reverse transcription-polymerase chain reaction for tyrosine hydroxylase mRNA

BACKGROUND

The aim of this study was to evaluate the changes of tumor cell contamination in bone marrow (BM) and peripheral blood (PB) during the clinical course of patients with advanced neuroblastoma by detecting tyrosine hydroxylase (TH) mRNA to clarify the appropriate source and time for harvesting hematopoietic stem cells for transplantation.

METHODS

A total of 15 patients with Stage IV neuroblastoma were studied. All 15 patients had peripheral blood stem cell (PBSC) samples and BM samples examined for TH mRNA by using the reverse transcription-polymerase chain reaction (RT-PCR) at the time of harvest. Nine of the 15 patients, also had BM and PB samples examined sequentially.

RESULTS

Comparing the 45 paired samples concurrently drawn, 16 of 28 BM samples (57.1%) and 4 of 28 PB samples (14.2%) obtained during complete remission (CR) were positive for TH mRNA (P < 0.01), whereas 17 of 17 BM samples (100%) and 14 of 17 PB samples (82.3%) obtained before CR was achieved were positive (not significant). The incidence of TH mRNA positivity was significantly lower in the samples obtained during CR than those obtained before CR was achieved (P < 0.0001 for PB samples, P < 0.01 for BM samples). At the time of PBSC harvesting, the incidence of TH mRNA positivity was lower in PBSC samples (3 of 15, 20%) than in BM samples obtained concurrently (10 of 15, 66.7%; P < 0.03).

CONCLUSIONS

These findings show that there is a substantial risk of tumor cell contamination in harvested PBSCs, although its incidence was lower than that in BM samples. We recommend that PBSCs would be better harvested during remission and should be examined for tumor contamination before use as a stem cell source.

Tyrosinase and related proteins in mammalian pigmentation

Tyrosinase is the key enzyme in pigment synthesis, initiating a cascade of reactions which convert the amino acid tyrosine to the melanin biopolymer. Two other tyrosinase-related proteins (TRP) are known, TRP-1 (probably DHICAoxidase) and TRP-2 (DOPAchrome tautomerase). These proteins show about 40% homology, and recent results have indicated that the genes might be derived from a common ancestor. We will discuss recent findings on genomic organization, and on the proteins and their presumed function, which is important for eumelanin synthesis in mouse and man.

Reverse transcriptase-polymerase chain reaction for expression of tyrosinase to identify malignant melanoma cells in peripheral blood

BACKGROUND

Circulating tumour cells in the peripheral blood may be important for haematogenous spread of disease. The detection of these cells may therefore be a poor prognostic indicator. Reverse-transcriptase polymerase chain reaction (RT-PCR) of target tumour-specific protein expression has been used as a sensitive and specific method for the detection of these tumour cells. Initial reports by our laboratory and other suggested RT-PCR amplification of the enzyme tyrosinase is a useful method for detection of melanoma cells in peripheral blood [1-3].

PATIENTS AND METHODS

In this report, we have evaluated the application of RT-PCR for tyrosinase mRNA as a detection method for melanoma cells in a series of 24 patients with advanced, metastatic malignant melanoma. A single round RT-PCR method is described.

RESULTS

The single round RT-PCR was as sensitive as previously described nested PCR methods, and had the advantage of reduced contamination risks. Blood samples from three out of the twenty-four patients were positive.

CONCLUSIONS

The frequency of tumour cell detection in peripheral blood from patients with advanced disease was lower than previously reported. It may be only small numbers of circulating tumour cells are present at any one time in the peripheral blood of patients with malignant melanoma. If this is the case increased sampling will improve detection frequency. Alternatively, dissemination of melanoma through peripheral blood may be a rare event. In our experience, RT-PCR for tyrosinase mRNA as a staging test for melanoma patients must be interpreted cautiously.

Detection of beta-human chorionic gonadotropin mRNA as a marker for cutaneous malignant melanoma

The beta chain of human chorionic gonadotropin (hCG) hormone is produced by fetal cells, gonadal cell tumors and several types of non-gonadal carcinoma. hCG is composed of an alpha and a beta chain, the latter of which can be used to distinguish the molecule from other related gonadotropin hormones. Detection of beta-hCG mRNA transcripts can be potentially useful as a marker to identify tumor cells. We devised a highly specific and sensitive assay to detect the atavistic expression of beta-hCG in cutaneous melanoma by RT-PCR. Twenty-four melanoma cell lines and 43 melanoma biopsies were evaluated for beta-hCG mRNA expression. An RT-PCR assay was developed to specifically distinguish beta-hCG poly-A mRNA from other related gonadotropin beta chains. This was performed by endonuclease digestion of a unique Sty 1 site in the beta chain, followed by Southern blot analysis with a beta-hCG cDNA probe. Of the 24 melanoma cell lines analyzed, 18 expressed beta-hCG mRNA. Analysis of melanoma biopsy specimens revealed beta-hCG mRNA expression in 17/25 melanoma-positive TDLN, and in only 5/15 non-lymphoid melanoma metastases. Beta-hCG mRNA expression had a 53% correlation to tyrosinase mRNA, a predominant melanoma marker. Beta-hCG mRNA was not detected in normal donor PBL and normal lymph nodes. Detection of beta-hCG mRNA expression may be a useful molecular marker to define a subset of malignant melanoma.

Identification of lymph node metastases by use of polymerase chain reaction (PCR) in melanoma patients

Diagnosis of clinically suspected lymph node metastases in melanoma patients can be confirmed with high sensitivity and specificity by fine needle aspiration (FNA) cytology. However, small lymph nodes or haemorrhagic metastases may yield negative or unevaluable cytology. We tested whether the sensitivity and specificity of presurgical diagnosis could be improved by a polymerase chain reaction (PCR) method, identifying tyrosine-mRNA in samples obtained by fine needle aspiration (FNA-PCR). PCR was positive in 17 of 18 histopathologically proven melanoma metastases, while conventional cytopathology detected 16 of 18. 4 of 9 disease-free melanoma patients with negative FNA cytology had positive PCR results, but controls gave negative results. FNA-PCR analysis cannot be recommended as superior to conventional FNA cytological examination. Whether the positive FNA-PCR in four of the nine clinically unsuspicious regional lymph nodes correlates with earlier disease progression or indicates lower specificity of the method will need further investigation.

Incomplete expression of the tyrosinase gene family (tyrosinase, TRP-1, and TRP-2) in human malignant melanoma cells in vitro

Sequence analysis of two clones found repressed in melanoma cell lines in earlier studies showed 9F2 to be identical with the TRP-1 gene and 6F5 with TRP-2 containing a long untranslated 3' end. For further investigation of the expression of the tyrosinase gene family in normal and malignant melanocytic cells, a series of melanoma cell lines and of cultured melanocytes were analyzed by Northern blotting and by reverse transcriptase-polymerase chain reaction (RT-PCR). The Northern blots were probed with cDNA fragments specific for TRP-1, TRP-2, and tyrosinase, for nested tyrosinase-PCR the outer primers specified a 284 bp and the nested primers a 207 bp fragment. Investigations on 14 established melanoma cell lines grown in different media compared with seven normal human melanocyte (NHM) cultures revealed that all three pigment genes were expressed in NHM, whereas pigment gene expression was found repressed in nearly all melanoma cell lines and was completely absent in 4 of 14 specimen. In particular, tyrosinase and TRP-2 genes were found always to be expressed together, and TRP-1 mRNA alone was absent in four melanoma cell lines. Negativity of cultured melanoma cells for tyrosinase mRNA was confirmed by nested RT-PCR, and gene deletion was ruled out by genomic Southern blots. The gene expression seemed independent from the type of medium used for cultivation. These findings indicate repressed or lacking expression of pigment genes in melanoma cell lines, most likely due to regulatory mechanisms, and that differences may exist between tyrosinase and TRP-2 on one hand and TRP-1 on the other. Overall, it seemed that RT-PCR for tyrosinase has limited value for identifying melanoma cells in the peripheral blood of melanoma patients; TRP-1, TRP-2, and other, additional markers may be required.

Dendritic cells generated from peripheral blood transfected with human tyrosinase induce specific T cell activation

Peptides of melanosomal proteins have recently been shown to be recognized in an HLA-restricted mode by specific cytolytic T lymphocytes in melanoma patients. Dendritic antigen-presenting cells (DC) are considered to be the most effective stimulators of T cell responses, and the use of these cells has therefore been proposed to generate therapeutic responses to tumor antigens in cancer patients. We, therefore, generated DC from peripheral blood of normal donors in the presence of granulocyte/macrophage colony-stimulating factor and interleukin-4. Flow cytometric analysis of the cells during a 2-week culture revealed a loss of CD14 and CD34 expression, a concomittent increase of CD1a, CD11a,b and c, CD44, CD45, CD54, HLA-class I and II, and intermediate levels of CD26, CD80 and CD86. Cultured DC stimulated proliferation of allogeneic T cells and induced a marked, up to 20-fold, stimulation of T cell proliferation after pulsing with tetanus toxoid. To achieve independence of already-identified antigenic peptides presented in HLA class I-restricted fashion, which limits the general applicability of such peptides for vaccination of melanoma patients, we tested whether DC are transfectable with eukaryotic expression plasmids. DC transfected with two reporter genes (CAT, beta-galactosidase) using a liposome-based transfection technique, exhibited only low levels of enzymatically active proteins, but were able to degrade rapidly intracellular proteins and to process peptides efficiently. Chloramphenicol acetyltransferase as well as tyrosinase mRNA were detectable after transfection by reverse-transcriptase-polymerase chain reaction, and enzyme activities became measurable. Furthermore, DC transfected with the tyrosinase gene were able to induce specific T cell activation in vitro, indicating appropriate peptide processing and presentation in DC after transfection. These data suggest new approaches to future tumor vaccination strategies.

Highly-sensitive identification of alpha-fetoprotein mRNA in circulating peripheral blood of hepatocellular carcinoma patients

In order to capture hepatocellular carcinoma (HCC) cells in circulating peripheral blood, we made analysis to see if alpha-fetoprotein (AFP) mRNA exists in the peripheral blood obtained from patients with HCC and also, as a control, from hepatitis-viral-marker-positive patients without HCC and a healthy volunteer. As the number of HCC cells in peripheral blood and the quantity of AFP mRNA are expected to be very small, the analysis was performed by the reverse transcription followed by an original three-step polymerase chain reaction. By this highly-sensitive method, 5 of 7 HCC patients were positive for AFP mRNA. These 5 positive patients consisted of three with clinically apparent recurrence, one preoperative patient with tumor thrombus in the portal vein and one recurrence-free patient who developed clinically detectable recurrence three months after this analysis. Neither 4 patients with positive viral markers nor a healthy volunteer was positive. The results suggest that detection of AFP mRNA from HCC patients' peripheral blood by our highly-sensitive RT-PCR may be a practical and powerful tool to diagnose the preoperative spreading of HCC and to monitor its recurrence.

Sensitive detection of occult Ewing's cells by the reverse transcriptase-polymerase chain reaction

Recently, Ewing's tumours have been shown to carry specific hybrid transcripts resulting from the fusion of the EWS gene with FLI-1 or ERG genes. Based on the sensitivity and specificity of the detection of these alterations by the reverse transcriptase-polymerase chain reaction technique, we have developed an assay to search for small numbers of Ewing cells in various sites from patients with Ewing's tumour. This method enables the detection of fewer than one tumour cell per million blood mononuclear cells. A total of 28 primary sites and 51 peripheral samples from 36 patients were investigated. Tumour cells could be detected in 4/18 blood samples, 4/15 bone marrow aspirates and 2/18 peripheral stem cell harvests. EWS/FLI-1 and EWS/ERG transcripts being observed in eight and two cases respectively. The type of fusion transcript detected in peripheral site(s) was identical to that observed in the primary site. At diagnosis 5/16 patients (31%) demonstrated either circulating tumour cells or/and occult bone marrow metastasis. After induction therapy, tumour cells were detected in 3/21 patients. This highly sensitive method should be a relevant tool to allow a more accurate clinical assessment of the dissemination of Ewing's tumours.

The detection of melanoma cells in peripheral blood by reverse transcription-polymerase chain reaction

Both cutaneous and uveal melanoma undergo haematogenous dissemination. Detection of tyrosinase mRNA by reverse transcription-polymerase chain reaction (RT-PCR) has been described as an extremely sensitive way of detecting circulating viable melanoma cells in the peripheral venous blood, and this technique may be of value in the early detection of dissemination. Also, it has been suggested that surgical manipulation of the eye, such as occurs during enucleation, can provoke uveal melanoma dissemination. The purpose of this study was to evaluate whether tyrosinase mRNA is detectable in the peripheral blood of patients with uveal and cutaneous melanoma and in patients with uveal melanoma undergoing surgical procedures on the eye harbouring the tumour. Venous blood samples from 36 patients diagnosed as having active uveal melanoma and from six patients with advanced metastatic cutaneous melanoma were analysed. In addition, blood samples were spiked with known numbers of cells from three cell lines and four primary uveal melanoma cultures. The reported sensitivity of the technique was confirmed, with an ability to detect down to one cell per ml of blood. All 51 blood samples from the 36 patients with uveal melanoma were negative, and this included 20 perioperative blood samples. The test was also negative for the six patients with advanced cutaneous melanoma. There were two positives among 31 control samples analysed. This study demonstrates that there are far fewer circulating viable melanocytes than has been previously supposed in patients with melanoma and that the RT-PCR is of no clinical value in detecting metastatic melanoma disease. There was no evidence for surgery causing a bolus of melanoma cells to enter the peripheral circulation.

Diagnosis of micrometastases by the amplification of tissue-specific genes

Micrometastases of solid tumors are most commonly detected by immunocytochemistry using monoclonal antibodies directed against tissue-specific gene products like cytokeratin-18 (CK-18) and the carcinoembryonic antigen (CEA). While CK-18 is a marker for epithelia in general, CEA is mainly employed in the detection of gastrointestinal and breast carcinomas. To improve the sensitivity and specificity of micrometastasis detection, we planned to establish polymerase chain reaction (PCR) assays for both markers. Here we provide strong evidence for the existence of a CK-18 pseudogene, since specific amplification (i) was readily obtained from healthy bone marrow donors, (ii) did not require reverse transcription of CK-18 mRNA and (iii) was not abolished by RNase treatment. Using a CK-18-specific probe, Southern blot analyses revealed identical-size fragments for both genomic DNA and a CK-18 cDNA after digestion with appropriate restriction enzymes. On the other hand, the amplification of CEA mRNA (i) was never observed in bone marrow samples of healthy donors or patients without solid tumors, (ii) required intact mRNA and the reverse transcriptase reaction, and (iii) could not be obtained after RNase treatment. In reconstitution experiments, single CEA-expressing tumor cells were reliably detected among 2 x 10(7) normal bone marrow cells. We conclude that, due to the presence of pseudogene(s), PCR-based detection systems are not readily suitable for CK-18, while the CEA mRNA amplification should provide a sensitive and specific test for the presence of ectopic, and hence presumed malignant, CEA-expressing cells in body fluids.

Sensitive detection of circulating hepatocellular carcinoma cells in peripheral venous blood

BACKGROUND

This study was performed to develop a sensitive method for the detection of circulating hepatocellular carcinoma (HCC) cells in peripheral blood, in advance of the diagnosis of distant metastasis of HCC by conventional means.

METHODS

Peripheral blood (5 ml) samples were obtained from 64 patients with HCC and from 48 control subjects (31 patients with benign liver disease, 8 with metastatic liver cancer, and 9 with normal liver function). To identify HCC cells in peripheral blood, liver-specific human alpha-fetoprotein (hAFP) mRNA was amplified from total RNA extracted from whole blood by reverse transcriptase-polymerase chain reaction.

RESULTS

Human alpha-fetoprotein mRNA was detected in 23 blood samples from the HCC patients (23/64, 36%), in 17 patients in whom there was no clinical evidence of distant metastasis. In contrast, there were no control patients whose samples showed detectable hAFP mRNA in the peripheral blood. The presence of hAFP mRNA in blood seemed to be correlated with the stage (by TNM classification) of HCC, the serum hAFP value, and the presence of intrahepatic metastasis, portal vein thrombosis, and/or distant metastasis.

CONCLUSIONS

Reverse-transcriptase polymerase chain reaction is a very sensitive method for detecting circulating HCC cells. With this technique, important information for the management of HCC can be acquired, such as the indications for orthotopic liver transplantation in HCC patients. Moreover, use of this detection method may encourage investigation of the mechanism of metastasis in HCC.

Detection of epithelial cancer cells in peripheral blood by reverse transcriptase-polymerase chain reaction

Circulating cancer cells in the blood play a central role in the metastatic process. Their number can be very small and techniques for their detection need to be both sensitive and specific. Polymerase chain reaction (PCR) has been successfully used to detect small numbers of tumour cells in haematological cancer in which abnormalities in DNA are sufficiently consistent to make this possible. For most solid tumours this not yet feasible. However, we have found that reverse transcriptase (RT)-PRC for tissue-specific gene expression is a useful technique for identifying small numbers of circulating cells in melanoma and neuroblastoma patients. In this report we describe detection of colon carcinoma cells by RT-PCR using CK 20 mRNA as a marker. Unlike other cytokeratin genes examined (CK 8 and CK 19), CK 20 was not transcribed in normal haematopoietic cells. This suggests a role for RT-PCR in the detection of colon carcinoma metastasis in blood and bone marrow, using CK 20 as the target gene. Future analysis of clinical material will determine the clinical significance of this technique.

Tumour diagnosis by PCR-based detection of tumour cells

Tumour cells shed from solid primary tumours can be detected by the polymerase chain reaction (PCR) based on the selective amplification of mutated tumour genes or of genes expressed in a tissue specific manner. When tumour specific alterations are amplified, few tumour cells can be detected in excess of normal cells derived from the same tissue. Thus, malignant cells can be detected specifically in pancreatic juice, stool, urine, and sputum. Here we describe the adaptation of the mutant enriched PCR in conjunction with the introduction of artificial primer mediated restriction sites to the selective amplification of mutant K-ras genes in stool samples from patients with colorectal carcinomas. In reconstitution experiments, down to 10 colorectal carcinoma cells could be detected in 100 mg of stool. For the diagnosis of micrometastatic disease, a sensitive and specific technique was established based on the reverse transcription of mRNA specific for the carcinoembryonic antigen followed by the amplification of the cDNA (RT-PCR). Attempts to establish a specific RT-PCR for cytokeratin-18 failed because of the existence of at least one processed pseudogene.

Early clinical evaluation of neuroblastoma cell detection by reverse transcriptase-polymerase chain reaction (RT-PCR) for tyrosine hydroxylase mRNA

Disseminating disease in neuroblastoma is of considerable clinical importance. Detection of circulating neuroblastoma cells using tyrosine hydroxylase (TH) as a tissue-specific target for reverse transcriptase-polymerase chain reaction has proved to be a sensitive and specific method for the detection of contaminating tumour cells in peripheral blood. The aim of this study was to report the early clinical observations made using this technology in neuroblastoma patient blood samples. A strong association was found between the detection of neuroblastoma cells in circulation with the detection of neuroblastoma in bone marrow. This method may be of use to monitor disease status and identify early signs of relapse in clinically disease-free patients. These results show that RT-PCR detection of TH mRNA is a relatively noninvasive, sensitive method for the detection of circulating tumour cells in neuroblastoma patients.

Detection of submicroscopic lymph node metastases with polymerase chain reaction in patients with malignant melanoma

BACKGROUND

The presence or absence of lymph node metastases in patients with malignant melanoma is the most powerful prognostic factor for predicting survival. If regional nodal metastases are found, the 5-year survival for the patient decreases approximately 50%. If the presence or absence of regional nodal metastases will determine which patients receive formal dissections or which patients enter adjuvant trials, then a technique is needed to accurately screen lymph node samples for occult disease. Routine histopathologic examination routinely underestimates the number of patients with metastases. This study was initiated to develop a highly sensitive clinically applicable method to detect micrometastases by examining lymph nodes for the presence of tyrosinase messenger RNA (mRNA). The hypothesis was that if mRNA for tyrosinase is found in the lymph node preparation, that finding is good evidence that metastatic melanoma cells are present.

METHODS

The assay is accomplished using the combination of reverse transcription and double-round polymerase chain reaction (RT-PCR). The amplified samples are examined on a 2% agarose gel and tyrosinase cDNA is seen as a 207 base pair fragment. Lymph node preparations from 29 patients who were clinically stage I and II and undergoing elective node dissections were analyzed both by standard pathologic staining and RT-PCR.

RESULTS

Eleven of 29 lymph node (38%) samples from 29 patients with intermediate thickness melanoma were pathologically positive. Nineteen of the 29 lymph node preparations (66%) were RT-PCR-positive, and these included all of the pathologically positive samples, so that the false-negative rate was 0. In a spiking experiment, one SK-Mel-28 melanoma cell in a background of one million normal lymphocytes could be detected, thus indicating the sensitivity of this method. In addition, analysis by restriction enzyme mapping showed that the amplified 207-bp PCR product produced is part of the tyrosinase gene sequence.

CONCLUSION

The RT-PCR method is an extremely sensitive, reproducible, and efficient technique for the identification of micrometastases in patients with melanoma and could be widely applicable. If clinical correlation is obtained, staging of the melanoma patient becomes more accurate, and treatment becomes more standardized and rational, because all those patients who have evidence of nodal disease can be identified so that they may benefit from more extensive surgery (formal node dissections) or adjuvant therapies. Based on these results, RT-PCR could be a powerful tool to detect micrometastatic melanoma.

Detection of alpha-fetoprotein mRNA, an indicator of hematogenous spreading hepatocellular carcinoma, in the circulation: a possible predictor of metastatic hepatocellular carcinoma

We attempted to detect circulating hepatocellular carcinoma by demonstrating hepatocyte-associated mRNA in the nuclear cell component of peripheral blood using nested reverse transcription-polymerase chain reaction because of the extremely small number of tumor cells in the circulation. Albumin mRNA was demonstrated not only in the liver tissue (hepatocytes) and HepG2 cells but also in nuclear cells of the blood from normal healthy volunteers (neutrophils and lymphocytes) by reverse transcription-polymerase chain reaction. In contrast, alpha-fetoprotein mRNA was demonstrated in the liver tissue, as well as in HepG2 cells, but not in peripheral blood of normal healthy volunteers, indicating the possibility of using alpha-fetoprotein mRNA for detection of benign and malignant hepatocytes among the population of neutrophils and lymphocytes. alpha-Fetoprotein mRNA in peripheral blood was detected in 17 of 33 cases of hepatocellular carcinoma (52%), 2 of 13 cases of cirrhosis (15%) and 2 of 17 cases of chronic hepatitis (12%). alpha-Fetoprotein mRNA was not demonstrated in 26 cases of normal healthy volunteers (0%). Among the patients with hepatocellular carcinoma, total volume of tumor tissue, maximum size of tumor and serum alpha-fetoprotein level were markedly increased in the patients with alpha-fetoprotein mRNA in blood. In addition, alpha-fetoprotein mRNA was detected in the blood of all 6 patients showing metastasis at extrahepatic organs (100%), in contrast to 11 of 27 cases without metastasis (41%). From these results, we conclude that the presence of alpha-fetoprotein mRNA in peripheral blood may be an indicator of circulating malignant or benign hepatocytes, which might predict hematogenous spreading metastasis of tumor cells in patients with hepatocellular carcinoma.

Neuroblastoma cell detection by reverse transcriptase-polymerase chain reaction (RT-PCR) for tyrosine hydroxylase mRNA

The presence of tumour cells in peripheral blood of neuroblastoma patients is of considerable clinical importance. Nucleic acid amplification offers an opportunity to detect very small numbers of such cells, but in neuroblastoma a frequent specific abnormality in the tumour DNA suitable for this purpose has yet to be identified. To facilitate the detection of such cells we have developed RT-PCR using tyrosine hydroxylase (TH) as a tissue-specific target gene. TH mRNA was detected in 3 neuroblastoma cell lines and in all neuroblastoma tumours examined, but was undetectable in peripheral blood from children without neuroblastoma. The method was highly sensitive, detecting 1-10 neuroblastoma cells per 10(7) blood cells. Thirty blood samples from 24 patients were analysed and results were compared with known disease status. At diagnosis 4/7 patient blood specimens were positive; the four positive samples were from stage-4 patients. In blood samples from these patients 6-8 weeks after the initiation of treatment, TH mRNA was undetectable. Of 7 samples taken at the time of clinical relapse, 5 were positive; 4 of these were from patients with evidence of disseminating disease. Of 16 blood samples from disease-free patients, 14 were negative and 2 were positive. One positive patient in this group subsequently had a clinical relapse. These results show that this technique is of value for detecting neuroblastoma cells in peripheral blood. The significance of these cells at diagnosis, during treatment or on follow-up requires further evaluation.

Molecular biology primer for the pediatric pathologist

Recent advances in the knowledge of molecular events of cell growth and differentiation have provided considerable gains to the understanding of neoplasia. Along with this understanding, molecular biology has yielded many new techniques of great potential for diagnostic use. This review illustrates, in general terms, current models of gene regulation, intracellular signal transduction, and the regulation of cell division that are relevant to pediatric pathologists. These concepts are used to examine the molecular pathology of three pediatric tumors: retinoblastoma, Wilms' tumor, and neuroblastoma. In addition, molecular biology techniques potentially useful to pediatric pathologists are discussed, with examples of some possible applications of these techniques. Hopefully, this review portrays the relevance of molecular biology to pediatric pathologists and serves as a useful guide to the interpretation of the molecular pathology literature.

Polymerase chain reaction: basic concepts and clinical applications in dermatology

The polymerase chain reaction (PCR) has been extensively used in basic science research, and the clinical potential of PCR is only now beginning to be realized. The PCR is based on the fundamental DNA replication process that occurs in every living cell. PCR is essentially an in vitro adaptation of the in vivo DNA copying process. Because PCR is so efficient at amplifying even picogram quantities of DNA, contamination with even trace amounts of nucleic acids can lead to the generation of unwanted DNA sequences and false-positive test results. Despite this, there has been rapid growth in the use of PCR in biomedical research and clinical diagnostics. PCR is the most sensitive test for herpes simplex virus, varicella-zoster virus, and human papillomavirus infections. Other diagnostic uses, including tests for genetic diseases, cancers, and other infectious diseases, are evolving.

Albumin messenger RNA as a marker of circulating hepatocytes in hepatocellular carcinoma

BACKGROUND/AIMS

Hepatocellular carcinoma is one of the most frequent malignancies. Liver transplantation is theoretically the treatment of choice because it eliminates both the hepatocellular carcinoma and the cirrhosis. High frequency of relapse observed after liver transplantation may be explained by the existence of undetectable metastasis before transplantation. The aim of this study was to determine whether albumin messenger RNA (mRNA), a specifically hepatocyte-expressed gene, could be a marker of metastasis in hepatocellular carcinoma.

METHODS

Albumin mRNA from circulating malignant hepatocytes was detected in the blood by reverse transcription followed by enzymatic amplification.

RESULTS

Albumin mRNA was found in the blood of 3 patients with histologically proven metastatic hepatocellular carcinoma and in 9 of 21 patients with hepatocellular carcinoma and undetectable metastases, giving a percentage rate of 43, similar to the relapse rate following liver transplantation for hepatocellular carcinoma. None of the 8 patients with secondary liver cancer had detectable albumin mRNA.

CONCLUSIONS

These results suggest that patients with hepatocellular carcinoma and no detectable albumin mRNA in the blood may be a subgroup with a low risk of relapse following liver transplantation.

Hematogenous spread of malignant melanoma cells in different stages of disease

Patients with malignant melanoma and distant metastases generally have an unfavorable prognosis, with a median survival of about 6 months. The mechanisms of hematogenous spread and implantation of melanoma cells are, however, poorly understood, because the standard diagnostic methods are not sensitive enough to detect oligocellular micrometastases. Recently a method using reverse transcription and polymerase chain reaction to determine tyrosinase mRNA in peripheral blood, which indicates the presence of circulating melanoma cells, has been developed. We utilized this assay to examine blood samples of 56 patients with malignant melanoma in different stages of disease. In one of 10 patients in stage I (localized disease) and in six of 17 patients with regional lymph nodes metastases (stage II) tyrosinase mRNA was detected. Tyrosinase transcripts were found in all 29 patients with distant metastases (stage III). Interestingly, tyrosinase mRNA was also detected in six patients with metastatic amelanotic malignant melanoma. In contrast, tyrosinase mRNA was not detectable in any of 39 healthy subjects or 17 patients with other malignancies. These findings may be helpful to define a patient group at high risk for systemic spread of disease.

Tyrosinase gene expression in human tissues

The occasional occurrence of primary extra-cutaneous malignant melanomas (MM) has led to the hypothesis that melanocytes derived from the neural crest may be arrested in their migration and may undergo an in situ malignant transformation. However, aggregates of nevus cells have only rarely been identified by histological examination in a few organs other than skin and eye. Tyrosinase is a melanin biosynthetic enzyme that is considered one of the most specific markers of melanocytic differentiation. We have attempted to detect cells committed to the melanocytic lineage, in human tissues, by means of tyrosinase gene expression. Total RNA was extracted from normal and neoplastic tissues and analyzed using a highly sensitive reverse transcription PCR assay with primers specific for the tyrosinase gene. Peripheral blood mononuclear cells (PBMC) from healthy subjects were used as negative controls. Tyrosinase transcripts were identified in a wide range of normal organs such as skin, lymph nodes, antrum, colon, kidney, lung, testis, ovary, breast, and peripheral nerve. Tyrosinase RNA was also detected in neoplastic samples including benign cutaneous nevi, lymph nodes involved by MM, breast carcinoma, liposarcoma, malignant lymphoma, and schwannoma. PBMC from patients with metastatic MM were also positive, while no positivity was detected in blood specimens from patients with other cancers. Therefore, it appears likely that cells expressing the tyrosinase gene are present in a wide range of human tissues. Although these cells still have to be accurately identified, one could propose that they might correspond to either fully differentiated melanocytes, melanocytic precursors, or Schwann cells bearing potentialities of melanocytic differentiation.(ABSTRACT TRUNCATED AT 250 WORDS)

The polymerase chain reaction. Applications in dermatology

Within the space of the last 5 years, application of the revolutionary in vitro method of deoxyribonucleic acid (DNA) amplification known as the polymerase chain reaction (PCR), has become ubiquitous. The rapidly increasing number of clinical and research articles utilizing this technology, both in the dermatologic and general medical literature, requires one to have at least a basic understanding of how the PCR is conducted, what it has to offer, and the potential shortcomings. Such knowledge will hopefully allow a more critical appraisal of an increasingly complex literature. This review aims to describe the methodology and medical applications of this powerful technique with special consideration to the increasing role PCR may have on dermatologic research and practice.

Detection and enumeration of circulating tumour cells in colorectal cancer

Immunocytochemistry was used in parallel with conventional cytology to detect circulating malignant epithelial cells in 42 patients undergoing resection for colorectal cancer. Preoperative peripheral and peroperative mesenteric venous blood samples were taken. Tumour cells were isolated on a density gradient and cytospins prepared. Slides were stained by conventional cytology (May-Grünwald-Giemsa) and by an indirect immunoperoxidase technique with the anticytokeratin antibody KG8.13. Using conventional cytology, definite morphological evidence of malignancy was observed in three patients and suspicious features in a further seven. Immunocytochemistry confirmed these findings in all three of the malignant but in only one of the suspicious cases. Counts of immunostained cytospins showed the concentration of tumour cells in blood samples from these four patients to be in the range 0-954 cells/ml. This study supports the use of immunological markers to detect and enumerate malignant cells. This method provides a powerful tool to investigate one aspect of the metastatic process.

Molecular genetics of human malignant melanoma

Due to a variety of known and unknown control mechanisms, the human genome is remarkably stable when compared to most other species. The long latency periods of most solid tumors, during which the cell undergoes malignant transformation, are presumably due to this stability. The molecular basis responsible for the induction of genetic instability and the resultant biological characteristics manifest in tumor populations is not well understood. The discovery of both oncogenes and tumor suppressor genes, however, has placed the phenomenon of human genome stability on a more solid conceptual footing. These types of genes clearly place multiple barriers to oncogenic transformation, and traversing these barriers apparently requires both time and the accumulation of genetic defects that cannot be corrected. The evolution of neoplasias can, therefore, be predicted to be due to: (1) consistent and progressive loss of tumor suppressor genes; (2) gene amplification, resulting in the over-expression of proteins that aid in tumor progression; (3) gene mutation, which alters the orderly biochemistry of the normal cell; (4) genes that allow a cell like the melanocyte to escape the confining nature of the epidermis and to invade through the dermis into the circulatory and lymphatic systems in order to disseminate itself to other organs (e.g., proteolytic enzymes, enzyme inhibitors, integrins, metastases genes, chemotactic factors etc.); (5) factors, perhaps such as TGF beta 2, that may impact negatively on MHC antigens and confuse host defense mechanisms; and (6) S.O.S.-type genes, which may be expressed as a direct response to the accumulating damage in an attempt to correct the damage, but that may then become part of the problem instead of the solution. The extraordinary plasticity and instability of the genome of a melanoma cell suggests an inordinate amount of genetic flux. In addition to activating and inactivating various genes, this constant shuffling and rearranging of the genome in neoplasms such as MM may be constantly altering gene dose. Cytogenetic and molecular biological studies have been the Rosetta stone for understanding the etiological relevant genetic events in human cancers. Genetic alterations fundamental to the pathology of MM have begun to be defined. Studies designed to understand these perturbations at the biochemical and organismic level are underway.(ABSTRACT TRUNCATED AT 400 WORDS)

Monoclonal antibodies in the detection and therapy of micrometastatic epithelial cancers

The initial promise of monoclonal antibodies as major therapeutic agents in human epithelial cancer has not been realized. Inaccessibility of cells in solid tumors due to factors such as the nature of the vascular endothelia and high pressure in the tumor are primarily responsible for the failure of antibody therapy. Although new strategies employing recombinant antibodies and immunoglobulins designed to actively engage the immune system may prove beneficial, micrometastatic tumor cells (at the stage of minimal residual disease) are likely to be the only suitable targets for antibody therapy. The diagnostic approaches to identify and characterize these cells and their use for prognosis and monitoring adjuvant immunotherapy is discussed.

Application of PCR to human gene detection

The advent of the polymerase chain reaction has stimulated the development of a number of rapid methods for characterizing human genes. In addition, the unprecedented level of sensitivity offered by some of these methods may prove to be of great value in the detection of minority cell populations. Over the past year, technical developments have been made in this area.