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

Melanoma patient staging: histopathological versus molecular evaluation of the sentinel node

Lymphatic mapping and sentinel lymphadenectomy provide a minimally invasive means of directly determining the status of the regional lymph nodes in all patients who have a primary melanoma >1 mm thick but no clinical evidence of nodal involvement. Since the histological status of the sentinel node (SN) has been shown to be the most important prognostic factor in primary melanoma patients, the World Health Organization has recently recommended that sentinel lymphadenectomy should become the new standard of care for primary melanoma patients. This paper reviews the literature with regards to developments in and the current status of SN evaluation. Developments in the histopathological versus molecular detection of melanoma nodal metastases are reviewed, with specific emphasis on the strengths, limitations and clinical significance of these techniques. Molecular evaluation of the SN offers several advantages over standard histopathological analysis. These include an improved sensitivity, the cost-effective use of multiple markers for the improvement of detection rate and prognosis, as well as being less labour-intensive and costly. Moreover, molecular analysis has the potential to allow estimation of tumour burden. We review the potential causes of technical false-negative and false-positive reverse transcription-polymerase chain reaction (RT-PCR) results and how these could be eliminated by a systematic approach consisting of (i) careful and systematic assay design, which would include efficient tissue homogenization, choice of reagents and molecular markers, primer design and the use of one-stage versus two-stage PCR; (ii) careful optimization of the RT-PCR parameters (in particular the PCR cycle number) through the use of appropriate control tissues; and (iii) aiming for high assay reproducibility and lastly by applying the necessary positive and negative controls with each batch of samples. We also review the significant improvement in patient prognosis and management that has been made possible by the development of sentinel lymphadenectomy and histopathological evaluation of the SN, and compare the clinical (predictive) value of histopathological analysis with that of RT-PCR. Although RT-PCR is able to detect additional, clinically significant SN metastases that are missed by routine histopathology, its current limitation is that it overestimates the number of patients who have clinically significant melanoma metastases. Therefore, we suggest and discuss appropriate steps that need to be taken in order to minimize these false-positives and make this molecular tool more acceptable for routine clinical use.

The role of ultrasound in detection and management of regional disease in melanoma patients

Melanoma follow-up programs are directed towards early detection of tumor recurrence. Because the majority of first relapses occur in the regional lymph node area, special focus is placed on this region using various techniques in addition to physical examination. During the last several years, particularly ultrasound B-scan has evolved as a technique of major importance for detection of such regional melanoma recurrences. The technique shows high sensitivity and specificity, discriminating regional or subcutaneous melanoma metastases from nonspecific nodes. Furthermore, suspicious findings can be evaluated quickly and reliably by the minimally invasive technique of ultrasound-guided fine-needle aspiration cytology (FNAC). For regional metastases located deeply or close to vulnerable structures, the new method of ultrasound-guided anchor-wire-marking facilitates subsequent surgery. In summary, ultrasound B-scan has become an essential technique in the follow-up of melanoma patients.

Polymerase chain reaction in the staging of solid tumors

Polymerasechain reaction (PCR) is a molecular biology technique that holds great promise as a way to perform molecular staging of cancer by detecting very early metastatic disease. Significant data suggest that PCR analysis may play an important role in the management of colorectal cancer in the future. However, for PCR staging of breast cancer, progress awaits identification of gene markers that have sufficient sensitivity and specificity. Within the next few years, the results of the Sunbelt Melanoma Trial and other ongoing studies will determine whether PCR evaluation of sentinel lymph nodes and peripheral blood cells has prognostic relevance in melanoma. The future of cancer management will likely revolve around the molecular staging of tumors, and PCR is but one method that may better define subgroups of patients that are appropriate candidates forvarious anticancer therapies.

Detection of micrometastasis in sentinel lymph nodes of patients with primary cutaneous melanoma

The technique of sentinel lymph node (SLN) biopsy has been demonstrated to be highly predictive for the detection of melanoma micrometastases in the regional lymph node basin. Therefore, the SLN was proposed to accurately reflect the lymph node status of patients with primary cutaneous melanoma. As the regional lymph node status is one of the most powerful predictors of survival in patients with primary melanoma, the histopathologic assessment is critically important for accurate staging. In approximately 20% (ranging from 9% to 42%) of patients with primary melanoma, the SLN was found to be tumor-positive by histopathology or immunohistochemistry. However, the true incidence of metastatic melanoma cells in (sentinel) lymph nodes is underestimated by histopathologic examination. Recently, the method of reverse transcription-polymerase chain reaction (RT-PCR) for tyrosinase mRNA has been used as a molecular marker for the presence of melanoma cells. Tyrosinase RT-PCR was demonstrated to significantly increase the detection of melanoma cells in SLNs as compared to histopathology. All lymph nodes positive by histopathology were shown to express tyrosinase by RT-PCR. Furthermore, tyrosinase transcripts were also detected in 36-52% of stage I and II melanoma patients with SLNs negative by histopathology. Importantly, the recurrence rate was significantly higher in patients with histologically negative SLNs who were found to be positive by RT-PCR than in patients with negative results by both techniques. These findings indicate that RT-PCR status of the SLN is more sensitive for detection of minimal melanoma disease than histopathology. Therefore, the RT-PCR status of the SLN may be suitable to improve melanoma staging and may serve as a prognostic factor in patients with primary cutaneous melanoma.

Examination of regional lymph nodes by sentinel node biopsy and molecular analysis provides new staging facilities in primary cutaneous melanoma

Histopathologic parameters of the primary tumor, such as Breslow's tumor thickness and Clark's level of invasion are the current basis for prognostic classifications of primary cutaneous melanoma. Once patients develop regional node metastasis, histopathologic features of the primary melanoma no longer contribute significantly to survival prediction. In this tumor stage, the extent of lymph node involvement is the main prognostic factor. This study addresses the question whether application of a highly sensitive molecular biology assay for detection of submicroscopic melanoma cells in sentinel lymph nodes may be suitable to improve melanoma staging. One hundred and sixteen patients with primary cutaneous melanoma with a total of 214 sentinel lymph nodes were enrolled. Sentinel lymph nodes were analyzed by histopathology including immunohistochemistry and by reverse transcription-polymerase chain reaction for tyrosinase. Patients were examined for tumor recurrences during a follow-up period of 19 mo (median). Disease-free survival probabilities were calculated and independent prognostic factors were determined by multivariate analysis. Using histopathology, micrometastatic nodal involvement was detected in 15 patients (13%). Of the 101 patients with histopathologically negative sentinel lymph nodes, 36 were reclassified by positive tyrosinase reverse transcription-polymerase chain reaction and 65 patients were still negative by reverse transcription-polymerase chain reaction. Recurrences were observed in 23 (20%) of 116 patients. These tumor recurrences were demonstrated in 10 patients (67%) with histopathologically positive sentinel lymph nodes, in nine patients (25%) with submicroscopic tumor cells detected by reverse transcription-polymerase chain reaction, and in four patients (6%) negative by both methods. The differences in recurrence rates were statistically significant (p = 0.01). In a multivariate analysis, histopathologic and reverse transcription-polymerase chain reaction status of the sentinel lymph node were demonstrated to be the only significant prognostic factors for predicting disease-free survival. Tyrosinase reverse transcription-polymerase chain reaction for the detection of minimal residual melanoma in sentinel lymph nodes is a powerful tool to determine patients who are at increased risk for subsequent metastasis. Moreover, a group of patients with high tumor thickness was identified by negative reverse transcription-polymerase chain reaction to be at low risk for recurrent disease. These data may have an impact on future tumor classifications of primary cutaneous melanoma.

Correlation of positive RT-PCR for tyrosinase in peripheral blood of malignant melanoma patients with clinical stage, survival and other risk factors

The clinical value of the reverse transcription polymerase chain reaction (RT-PCR) assay for tyrosinase in peripheral blood of melanoma patients is still under debate. A total of 212 blood samples from 212 melanoma patients in all clinical stages (AJCC) were examined. Erythrocytes were lysed prior to RNA extraction by phenol precipitation from 2.7 ml of blood. cDNA for tyrosinase PCR was synthesized using random hexamers. Positive tyrosinase RT-PCR results were obtained in 11% of 106 stage I patients, 18% of 56 stage II patients, 31% of 26 stage III patients and 67% of 24 stage IV patients. After a median follow-up of 36 months (range 26-41), stage III patients with positive RT-PCR for tyrosinase had a shortened disease-free interval as compared to negative patients (P < 0.01). In stage IV patients, median overall survival was 8 months in case of a positive RT-PCR in contrast to 12 months in case of a negative test. While univariate analysis showed sex and primary tumour location associated with positive RT-PCR, multiple regression analysis revealed clinical stage and detection of tyrosinase transcripts in peripheral blood as best prognostic factors. Hazard ratios for disease-free survival were 19.7 (confidence interval (CI) 8.53-45.5, P = 0.0001) for metastatic vs primary disease and 2.96 (CI 1.49-5.89, P = 0.002) for positive vs negative tyrosinase RT-PCR. The corresponding hazard ratios for overall survival were 97.0 (CI 12.7-741, P = 0.0001) and 4.33 (CI 1.69-11.1, P= 0.002). Our results emphasize the importance of tyrosinase RT-PCR testing in peripheral blood.

Detection of melanoma micrometastases in the sentinel lymph node and in nonsentinel nodes by tyrosinase polymerase chain reaction

The aim of our study was to investigate the metastatic pathways of melanoma cells in sentinel and other regional lymph nodes. The term "sentinel lymph node" means that the first lymph node of the draining site of a primary tumor is never bypassed in malignant melanoma. In this case lymph node dissection would be necessary only when melanoma cells are detected in the sentinel node. Tyrosinase reverse transcriptase-polymerase chain reaction was applied to search for metastatic melanoma in the sentinel lymph node and in further lymph nodes of a complete lymph node basin in patients who underwent lymph node dissection. In 24 patients with malignant melanoma the draining site of the tumor was marked by lymphoscintigraphy and by intraoperative injection of patent blue V in the area around the primary tumor. The lymph nodes of the affected basin were excised and prepared for histopathologic, immunohistochemical, and molecular biologic examinations. Regarding the sentinel lymph node, 10 of 24 patients showed morphologic evidence for metastases, three additional patients showed only tyrosinase transcripts. In 11 of these 13 cases we found one or more nonsentinel lymph nodes with morphologically detectable melanoma cells and/or tyrosinase mRNA. Interestingly, in seven of 24 patients a positive tyrosinase reverse transcriptase-polymerase chain reaction was received in nonsentinel lymph nodes, whereas the sentinel lymph node was negative, not only for all histologic examinations but also by tyrosinase reverse transcriptase-polymerase chain reaction. In five of seven patients of the latter group, gp100 reverse transcriptase-polymerase chain reaction was carried out, showing also gp100 mRNA in nonsentinel lymph nodes only. Our data indicate that the concept of the sentinel lymph node may miss micrometastases. Whether such micrometastases cause a recurrence or a metastasis of malignant melanoma, or can be destroyed by the immune system, remains to be clarified.

Detection of regional melanoma metastases by ultrasound B-scan, cytology or tyrosinase RT-PCR of fine-needle aspirates

Physical examination and ultrasound B-scan screening are important follow-up procedures in melanoma patients with regional disease. However, they do not allow definite diagnosis of suspicious lesions. Fine-needle aspiration cytology (FNAC) enhances the diagnostic accuracy in such patients but, unfortunately, reaches its technical limits, particularly when very small or necrotic lesions are examined. We therefore tested whether tyrosinase reverse transcription polymerase chain reaction (RT-PCR) of fine-needle aspirates (FNA-PCR) could help to increase diagnostic sensitivity. With clinical follow-up in 69 melanoma patients 81 regional lymph nodes were detected by ultrasound B-scan examination, nine of whom appeared to be palpable. Technically, FNAC was successful in all 81 lymph nodes, while FNA-PCR failed to obtain RNA at detectable levels in two lymph nodes of two patients. Of 79 lesions which have been completely evaluated by B-scan, FNAC and FNA-PCR, 44 proved to be melanoma metastases by histopathology, while the remaining 35 lesions were finally classified as non-specific lymph nodes. Of the 44 melanoma metastases 80% (n = 35) have been detected by B-scan, 90% (n = 39) by FNAC and 100% (n = 44) by FNA-PCR (P < 0.05 vs FNAC, P < 0.005 vs B-scan). In the subclass of lesions with diameters below 10 mm the sensitivities were 72% (n = 13), 78% (n = 14) and 100% (n = 18) respectively. In 35 regional lymph nodes classified as benign lesions, FNAC was always negative while FNA-PCR produced one positive result. Neither of these methods did produce false positive results in 15 control lymph nodes of non-melanoma patients. We conclude, that FNA-PCR might have superior sensitivity as compared to FNAC or ultrasound B-scan, particularly in melanoma lesions with diameters below 10 mm.

Sentinel lymphadenectomy in the management of primary cutaneous malignant melanoma. An update

The management of lymph nodes in melanoma patients who have no clinical evidence of nodal disease has changed dramatically with the development of selective lymph node biopsy. This procedure localizes the node in a regional basin most likely to contain a metastasis (the sentinel node) and averts the morbidity of unnecessary elective node dissection. This update reviews the rationale for this procedure and describes the methodology used by the surgeon and the pathologist. A progress report highlights the promise and limitation of this procedure. Sentinel node biopsy is currently the standard for staging select groups of melanoma patients, but the field is rapidly evolving and may eventually be surpassed by even newer molecular diagnostic techniques.

Lymph node micrometastases of cutaneous melanoma: increased sensitivity of molecular diagnosis in comparison to immunohistochemistry

The presence of regional lymph node metastases is one of the most significant prognostic factors for predicting survival in patients with clinical stage I or II cutaneous melanoma. For accurate staging of the primary tumor a sensitive technique is required to detect occult nodal micrometastases. This prospective diagnostic study was designed to evaluate the incidence of nodal micrometastases using nested reverse transcription-polymerase chain reaction (RT-PCR) for tyrosinase in comparison to immunohistochemical examination. Furthermore, the incidence of melanoma micrometastases detected by RT-PCR was analysed in correlation to major prognostic factors. A total of 466 regional lymph nodes from 79 patients with primary cutaneous melanoma (tumor thickness > 0.75 mm) were investigated. In 49 lymph nodes from 31 patients immunohistochemistry demonstrated melanoma metastases. Using tyrosinase RT-PCR, nodal micrometastases were detected in 136 lymph nodes from 52 patients including all lymph nodes positive by immunohistochemical examination. Out of the 417 lymph nodes negative by immunohistochemistry, 87 nodes (21%) were identified to express tyrosinase by the RT-PCR technique. Among the 48 patients negative by immunohistochemical assessment, 21 (44%) had nodal micrometastases (n = 40) using RT-PCR. All 68 lymph nodes from 46 non-melanoma patients serving as negative controls for tyrosinase RT-PCR were negative. The detection of melanocytic nodal micrometastases by tyrosinase RT-PCR is a highly specific method with a sensitivity significantly higher than that achieved by immunohistochemistry (p < 0.0001). Patients with nodal micrometastases identified exclusively by RT-PCR had significantly higher tumor thickness as compared to patients with negative results by RT-PCR (p < 0.01).

Utilization of polymerase chain reaction technology in the detection of solid tumors

BACKGROUND

Most cancer detection tests currently performed are based on either antibody assays to a marker protein with altered expression in cancer patients or on imaging studies to identify characteristic lesions. Generally, for a positive result, these detection assays require that a tumor have a significant volume of cancer cells. Advances in diagnostic techniques and technology may allow for cancer detection at earlier stages, when the tumor burden is smaller and potentially more curable. The molecular techniques of polymerase chain reaction (PCR) and reverse transcriptase PCR (RT-PCR) are highly sensitive methods for detecting a small number of cancer cells. Over the past few years, numerous clinical studies have used PCR techniques to detect physical alterations of genes, such as mutations, deletions, translocations and amplification, the presence of oncogenic viruses, and the expression of genes specific to tissue, cancer, and metastasis. The current status of PCR as a method for detecting marker genes in the management of solid tumors is reviewed.

METHODS

A review of the literature on the clinical utility of PCR and RT-PCR in the detection of solid tumor micrometastasis was conducted.

RESULTS

Amplification by PCR is a highly sensitive method to determine gene expression. A single cell expressing a tumor marker among 10-100 million lymphocytes can be detected by the PCR assay. This approach has been used to detect tumor cells in approximately 18 different solid tumor types, with melanoma and carcinoma of the breast and prostate the most widely investigated to date. PCR-based assays have been used to detect cancer cells in biopsies of solid tissue, lymph nodes, bone marrow, peripheral blood, and other body fluids. Several studies have reported a high specificity and sensitivity of tumor marker detection and a high correlation between PCR results and the presence of metastatic disease. However, in a few studies, PCR assays have not consistently demonstrated a higher sensitivity and specificity of detection than traditional modalities for many types of cancer. There has been a wide range in sensitivity and specificity among the studies, which may be partly attributed to the lack of uniformity among the PCR protocols used in different studies.

CONCLUSIONS

PCR can detect tumor marker-expressing cells that are otherwise undetectable by other means in patients with localized or metastatic cancer. Reports from various study groups have lacked uniformity in their protocols, and this has prevented adequate comparison. The clinical utility of this assay as a tool for the prognosis and management of cancer patients remains and area of active investigation. PCR is a powerful tool in the study of the biology of cancer metastasis and will likely serve as a useful adjunct to clinical decision-making in the future.

Utilization of polymerase chain reaction technology in the detection of solid tumors

BACKGROUND

Most cancer detection tests currently performed are based on either antibody assays to a marker protein with altered expression in cancer patients or on imaging studies to identify characteristic lesions. Generally, for a positive result, these detection assays require that a tumor have a significant volume of cancer cells. Advances in diagnostic techniques and technology may allow for cancer detection at earlier stages, when the tumor burden is smaller and potentially more curable. The molecular techniques of polymerase chain reaction (PCR) and reverse transcriptase PCR (RT-PCR) are highly sensitive methods for detecting a small number of cancer cells. Over the past few years, numerous clinical studies have used PCR techniques to detect physical alterations of genes, such as mutations, deletions, translocations and amplification, the presence of oncogenic viruses, and the expression of genes specific to tissue, cancer, and metastasis. The current status of PCR as a method for detecting marker genes in the management of solid tumors is reviewed.

METHODS

A review of the literature on the clinical utility of PCR and RT-PCR in the detection of solid tumor micrometastasis was conducted.

RESULTS

Amplification by PCR is a highly sensitive method to determine gene expression. A single cell expressing a tumor marker among 10-100 million lymphocytes can be detected by the PCR assay. This approach has been used to detect tumor cells in approximately 18 different solid tumor types, with melanoma and carcinoma of the breast and prostate the most widely investigated to date. PCR-based assays have been used to detect cancer cells in biopsies of solid tissue, lymph nodes, bone marrow, peripheral blood, and other body fluids. Several studies have reported a high specificity and sensitivity of tumor marker detection and a high correlation between PCR results and the presence of metastatic disease. However, in a few studies, PCR assays have not consistently demonstrated a higher sensitivity and specificity of detection than traditional modalities for many types of cancer. There has been a wide range in sensitivity and specificity among the studies, which may be partly attributed to the lack of uniformity among the PCR protocols used in different studies.

CONCLUSIONS

PCR can detect tumor marker-expressing cells that are otherwise undetectable by other means in patients with localized or metastatic cancer. Reports from various study groups have lacked uniformity in their protocols, and this has prevented adequate comparison. The clinical utility of this assay as a tool for the prognosis and management of cancer patients remains and area of active investigation. PCR is a powerful tool in the study of the biology of cancer metastasis and will likely serve as a useful adjunct to clinical decision-making in the future.