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Clinical Investigation |
1 Clinica Chirurgica 2, Università di Padova, Padova, Italy; 2 Clinical Trials and Biostatistical Unit, Istituto Oncologico Veneto, Padova, Italy; 3 Melanoma Unit, European Institute of Oncology, Milano, Italy; 4 Dermatochirurgia, Ospedale Bufalini, Cesena, Italy; 5 Dermatochirurgia, Ospedale S. Lazzaro-Molinette, Torino, Italy; 6 Clinica Chirurgica, Arcispedale S. Anna, Ferrara, Italy; 7 DermatologiaDermochirurgia, Ospedale Sestilli, Ancona, Italy; 8 Chirurgia Plastica, Università di Bari, Bari, Italy; 9 Chirurgia Dermatologica, Istituto Ricerca e Cura del Cancro di Candiolo, Candiolo, Italy; 10 Medicina Nucleare, Ospedale S. Chiara, Trento, Italy; 11 Divisione di Chirurgia 1, Istituto Regina Elena, Roma, Italy; 12 Anatomia Patologica, Università di Padova, Padova, Italy; 13 Medicina Nucleare 2, Azienda Ospedaliera di Padova, Padova, Italy; and 14 Chirurgia Plastica e Centro Ustioni, Azienda Ospedaliera di Udine, Udine, Italy; on behalf of the Italian Melanoma Intergroup (IMI)
Correspondence: For correspondence or reprints contact: Carlo Riccardo Rossi, MD, Dipartimento di Scienze Oncologiche e Chirurgiche, Sezione di Clinica Chirurgica, Università di Padova, Via Giustiniani 2, 35128 Padova, Italy. E-mail: carlor.rossi{at}unipd.it
| ABSTRACT |
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Key Words: lymphoscintigraphy sentinel node biopsy cutaneous melanoma quality control program
| INTRODUCTION |
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While biologic factors (e.g., Breslow thickness, mitotic rate, ulceration, and so on) predicting SN status have been extensively investigated (4,5), investigators have paid less attention to the impact of SNB technical variables on the SN identification rate and status (6).
In this article we present the results of an observational multicentric Italian trial on SNB, performed on behalf of the Italian Melanoma Intergroup (IMI), which enrolled >1,300 patients affected with primary cutaneous melanoma. This study was conducted with the main aim of diffusing the use of a common SNB protocol nationwide. As some aspects of the SNB technique wereand still arenot standardized worldwide, the protocol has left some room for variability in performing the procedure, such as the timing of lymphoscintigraphy, the number and site of the injections, and the radiotracer dose. This revealed a certain degree of technical heterogeneity among the participating centers, depending on institutional/personal preferences/beliefs, which allowed us to investigate the relative importance of such variability when affecting the outcome variablesthat is, the rate of SN identification, the number of excised SNs and the SN status.
To validate the study results, a quality control program (QCP) was conducted for the surgical and the histopathologic procedures.
| MATERIALS AND METHODS |
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All consecutive patients with lesions with a Breslow thickness of >1.0 mm or <1.0 mm with at least one of the following histopathologic featuresulceration, Clark level IVV, presence of regressionwere considered for lymphatic mapping and SN biopsy. Patients with clinical metastasis detected by palpation or ultrasound examination were excluded.
Patients
From January 2000 to December 2002, 1,313 patients with primary cutaneous melanoma were enrolled. Some variability in patient accrual (range, 7268 patients) appeared across the clinical centers, with 10 centers enrolling >50 patients.
There were 666 males (50.7%) and 647 females (49.3%), with a median age of 52 y (range, 1391 y). Tumor characteristics are reported in Table 1.
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Intraoperatively, the SN was located by using a handheld
-probe and the blue dyebased lymphatic mapping technique. After the induction of satisfactory anesthesia (local or general), Patent blue dye was intradermally injected around the excision biopsy site, and the area was massaged to promote lymphatic flow. When the primary lesion was located on the face or neck areas, vital dye was generally avoided if a wider excision was not indicated. After approximately 510 min, a handheld
-probe was used to identify the hot spots over the SN. A small incision was made directly over the hot spots and carried down through the skin and subcutaneous tissue into the node-bearing fat. Any blue-stained or hot node (defined as the hottest node), and any other node with at least 5-fold the background radioactivity, were excised and sent for pathologic analysis. Definitive wide excision of the primary cutaneous melanoma was performed, if required, after the SNB procedure.
SN Pathologic Evaluation
SNs were evaluated according to the protocol suggested by a panel of pathologists skilled in melanoma and SN evaluation. SNs were cut along their longitudinal axis in 2- to 3-mm-thick slices and embedded in paraffin blocks. At least 10 serial sections were obtained from each block and examined by conventional hematoxylineosin staining (sections 1, 3, 5, 7) and by immunohistochemistry using both S100 (sections 2, 4, 8) and HMB45 antibodies. Sections 9 and 10 were available for additional staining. A positive SN was defined as a lymph node containing melanoma cells detected by either hematoxylineosin or immunohistochemistry.
Micrometastases were defined as tumor deposit of
2 mm.
False-Negative Cases
Those patients with negative SNB who experienced lymph node metastasis in the same lymphatic basin(s) during the follow-up period were considered false-negative cases. The false-negative rate was calculated as the number of false-negative cases over the sum of the true-positive plus the false-negative cases.
Patients with signs of distant or in-transit metastases without lymph node relapse were not considered as false-negative.
Quality Control Program
A QCP on the SNB surgical procedure was performed by means of site visits performed during the study period. The QCP was organized in 2 steps: during the first phase, the 3 centers with the highest accrual audited the 3 centers with the second highest accrual and vice versa. During the second phase, the remaining centers with the lowest accrual were assigned to 1 of the 6 centers for an audit visit. All site visits occurred during a SNB procedure performed on a patient enrolled in the study. At the end of the visit, the surgeon in charge of the audit compiled a structured questionnaire regarding the procedure and assigned an overall judgment.
With regard to the pathologic evaluation of SN, the data center (Clinical Trials and Biostatisitical Unit, Università di Padova [IOV-Padova]) randomly selected 5 patients for each participating center, 1 SN positive and 4 negative, at the end of the study. The histologic samples were submitted to a panel of pathologists who reviewed them with no knowledge of findings. The panel included 5 pathologists involved in the study and 1 external reviewer.
For each case, the procedural quality was assessed, scoring the hematoxylineosin sections, the immunohistochemistry sections, and the number of sections, according to a prespecified scale. Finally, a diagnosis about the SN status was issued for each case.
Statistical Analysis
All data were collected and analyzed by the same data center (Clinical Trials and Biostatisitics Unit, IOV-Padova). To verify the association between the number of lymphoscintigraphy-detected and excised SNs the Kendall test was used.
To evaluate any univariate association between the number of SNs removed, or the SN status, and each of the characteristics of the lymphatic mapping, the ANOVA and the
2 test were used whenever appropriate.
A logistic regression model, with a stepwise selection procedure, was used to examine the joint effect of the technical variables on SN metastasis.
A multiple linear regression model was used to evaluate the independent association between the technical covariates and the number of excised nodes. The variables considered for the analysis were the maximal length of primary tumor excisional biopsy, number of radiotracer injections, volume of radiotracer injected, dose of radiotracer, and center's case load.
Statistical significance was determined using an
-level of 0.05 and 2-sided tests. Microsoft Access database software (Microsoft Corp.) and SAS statistical software (SAS Institute Inc.) were used for the compilation of data and statistical analysis, respectively.
| RESULTS |
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-b = 0.57059; P < 0.0001). Only 1 SN was removed in 591 patients (45.4%). The axilla was the site of the SN in 52% of the cases, followed by the groin (37.6%).
SN Status
SN positivity rate was 16.9% (220 of 1,304 patients), most patients having only 1 positive SN (80.4%). The positivity rate per basin (axilla, 13.9%; groin, 18.1%; laterocervical, 12.5%; other sites, 6.8%) and for primary site (head and neck, 15.47%; trunk, 16.36%; superior limbs, 14.46%; inferior limbs, 18%) was not significantly different.
Micrometastases were present in 84 of the 220 patients with positive nodes (38.2%).
Lymphoscintigraphy Variables
The variability of the lymposcintigraghic aspects of the SNB procedure is illustrated in Table 3. One or 2 radiotracer injections were performed in 697 patients and 3 or 4 in the remaining 587. An injected total volume of 0.5 mL was used the most frequently. There was some variability in the radiotracer dose used, mainly because of the different time intervals between the lymphoscintigraphy and the surgical procedure.
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3 were performed (P = 0.002); as for the total volume of radiotracer, the mean number of LS-detected SNs was 1.8 when <0.5 mL of the total injected volume was used and was1.7 when
0.5 mL was injected (P = 0.047).
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The false-negative rate did not differ among centers with large and small case loads. In the 172 patients enrolled across the centers with a case load of
50, there were 7 false-negative cases (12.7%; 95% CI, 3.9%21.5%), whereas in the 837 patients enrolled in the centers with the major case load, there were 31 false-negative cases (15.3%; 95% CI, 10.3%20.2%).
No technical variable was correlated with the occurrence of disease relapse in the same lymphatic basin(s) during observation.
Quality Control Program
With reference to surgery, the site visit was performed in 20 clinical centers. In the remaining 3 centers the visit was not performed because of logistic problems. The overall judgment was generally positive, as shown in Table 6, with only 1 center ranking "sufficient" because of insufficient staging procedures performed on the patient before the SNB took place.
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| DISCUSSION |
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According to the original definition by Morton et al., the SN is the lymph node that receives direct drainage from the primary lesion (1). Therefore, after diagnostic biopsy, lymphoscintigraphy is performed in most patients with cutaneous melanoma to identify the SN and differentiate it from nonsentinel nodes of the same lymphatic basin (i.e., second- or third-tier lymph nodes; Figure 1) (10). In the 1990s, the IMI formulated a protocol on SNB and gathered together 23 Italian clinical centers to perform an observational prospective study with the main aim of spreading a common protocol nationwide. The surgical guidelines (including lymphatic mapping with blue dye) for SNB and the histologic examination were quite stringent, as they were taken primarily from Morton's experience (1). By contrast, a certain degree of variability in the lymphoscintigraphy technique (e.g., the number and site of radiotracer injections and the radiotracer dose/concentration) was considered acceptable, as reported in a survey performed among European centers performing the SNB procedure (11). At that time, the level of reproducibility of lymphoscintigraphy was approximately 85% and the procedure was already considered the gold-standard to detect the SN in melanoma patients, whereas the additional use of blue dye was suggested whenever difficulties in identifying the SN were anticipated by lymphoscintigraphy (1113). We have therefore considered blue mapping as a complementary procedure and did not further investigate its impact on the outcome of SNB.
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The results achieved in our study with regard to the SNB procedure (identification, positivity, and false-negative rate of 99.3%, 16.9%, and 14.7%, respectively) are comparable with those reported in literature (1521), thus confirming the validity of this technique. Interestingly, we observed that the case load did not affect the outcome of the surgical procedure, as there was no significant difference in SN detection, positivity, and false-negative rates among the participating centers enrolling <50 or >50 consecutive patients.
Overall, these findings support the idea that SNB can be reliably performed once an adequate learning phase has been completed. Nevertheless, there is still room for improving this technique. Although increasing the SN identification rate (presently ranging between 98% and 99%) is rather unlikely, it seems more reasonable to focus on the possibility of lowering the false-negative rate (calculated as the number of false-negative cases over the sum of true-positive and false-negative cases), which ranges from 13% to 18% in the largest series reported so far (9,15,18), by modifying some technical details. For instance, some investigators have recently demonstrated that the use of carbon dye for lymphatic mapping and a more accurate protocol of SN pathologic or polymerase chain reactionbased examinations can identify SN metastasis with higher accuracy (2224). Improving the reproducibility of lymphoscintigraphy might also be useful for this purpose (1113,17). The high number of patients enrolled in our study and the variability in performing lymphoscintigraphy prompted us to investigate whether any technical detail might have an influence on this issue. By considering the most common parameters that might affect the results of lymphoscintigraphy, we found that only the number of radiotracer injections significantly affects the selectivity (i.e., the number of SNs removed) and the sensitivity of this procedure. In fact, when >3 radiotracer injections were used, a lower number of SNs was found (1.7 vs. 2.2; P < 0.0001), whereas the proportion of positive nodes was higher (19.2% vs. 14.1%; P = 0.021), although it was not retained in the multivariate analysis, when the tumor thickness variable was included in the model.
Furthermore, in our experience, the different positivity rate observed in the 2 study groups (higher vs. lower radiotracer injection number) did not translate into a significant difference in the false negativity rate. However, given the low number of false-negative cases in our series, a longer follow-up is warranted to verify this finding.
A hypothetic explanation for the correlation between radiotracer injection number and SNB outcome could be the microanatomy and physiology of cutaneous lymphatic vessels. Initial lymphatic capillaries are formed by overlapping endothelial cells with an incomplete basement membrane and do not have a complete muscle layer. The flow through these vessels can be markedly enhanced by increasing the interstitial pressure (e.g., through massage) (25,26). According to this hypothesis, an increased interstitial pressure can favor the entry of the radiotracer into the lymphatics and eventually the corresponding lymph nodes (10). For the same reason, the intradermal injection of relatively large volumes of radiotracer (using a low number of injectionsthat is, <3) might increase the interstitial pressure and, consequently, the amount of radiocolloid into each lymphatic vessel (Fig. 1A): this would increase the number of lymph nodes reached by the radiotracer (second-tier lymph nodes) and, ultimately, the number of excised SNs. Moreover, a few injections might not be enough to enter all the lymphatic capillaries draining a given skin area and, therefore, to visualize an adequate number of SNs (12,13,27). By contrast, smaller radiotracer volumes, such as those achieved with a higher number of injections, might lead to visualization and excision of fewer second-tier lymph nodes (Fig. 1B). In addition, the greater distribution of the injections along the scar might account for the visualization of peripheral lymphatic vessels used by metastatic cells to reach the draining lymphatic basin, thus accounting for the higher number of positive SNs detected and excised.
| CONCLUSION |
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| APPENDIX |
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Data Center
Pathology Panel
Participating Centers
| ACKNOWLEDGMENTS |
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| References |
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