Comparison of ^99mTc‐MIBI scintigraphy and sentinel node biopsy in the detection of occult lymph node metastases from cutaneous melanoma

ARTICLE

Auteur(s) : Omar ALONSO¹, Miguel MARTÍNEZ^{2, 3}, Lucía DELGADO^{2, 5}, Graciela LAGO¹, Cecilia JURI¹, Alejandra Larre BORGES^{2, 3}, María C. LOPES DE AMORIM¹, Daniela DE BONI^{3, 4}, José ESPASANDÍN⁴, Julio PRIARIO⁵

¹ Department of Nuclear Medicine, ² Department of Medicine, ³ Department of Dermatology ⁵ Clinical Hospital, University of Uruguay, Av. Italia s\n, Montevideo 11600, Uruguay, ⁴ Department of Clinical Oncology, National Institute of Oncology, Famaillá 3304, Montevideo 11600, Uruguay

Article accepted on 28\7\2003

Key words: Melanoma represents a significant and growing public health burden worldwide, being one of the remaining cancers with an increasing incidence rate [1]. It has been demonstrated that nodal metastases from cutaneous melanoma are not random events. Tumour spread within the regional draining basin has been shown to progress in an orderly fashion, and the first draining node (sentinel node) is the most likely to show metastatic involvement. Thus, the sentinel node histology accurately reflects the histology of the remainder of the lymphatic basin, it being rare for other nodes to contain melanoma cells [2]. Since the pioneering efforts of Morton et al. [3], sentinel lymph node biopsy (SLB) with previous lymphatic mapping by means of radiocolloid lymphoscintigraphy has been proposed by some authors as a routine method for staging the regional lymph nodes for patients with cutaneous melanoma [4]. A positive SLB has been found to carry greater prognostic significance than the Breslow thickness, and identifies those patients who might benefit from early therapeutic lymph node dissection, adjuvant interferon or vaccine treatment [5]. A number of standard imaging techniques including ultrasound, MRI, and CT mostly rely on active metastatic growth at lymph nodes, but normally sized nodes may contain malignant cells, and enlarged lymph nodes are not necessary malignant [6,7]. Besides, positron emission tomography (PET) using ¹⁸F‐fluoro‐2‐deoxy‐D‐glucose (FDG), based on hypermetabolism of glucose by tumour cells, has been shown to be effective in detecting regional and distant metastases in melanoma and other malignant diseases [8]. However, in pre‐treatment nodal staging of melanoma FDG PET has not proved to offer any significant advantage in diagnostic sensitivity [9‐12]. In the last few years, some teams have been studying the clinical value of ^99mTc‐methoxy‐isobutyl‐isonitrile (MIBI) scintigraphy for the evaluation of metastatic melanoma lesions. The technique proved to have potential for detecting subclinical recurrent disease, including lymph node metastases [13‐16]. No studies exist that compare ^99mTc‐MIBI scanning to histologic analysis of sentinel node tissues, the current gold standard for staging of regional node basins in patients with clinically normal lymph nodes. Therefore, we undertook a prospective investigation to evaluate the contribution of ^99mTc‐MIBI scintigraphy for detecting sentinel node metastases in patients with American Joint Committee on Cancer (AJCC) stage I‐II melanoma [17].

Patients and methods

We conducted a prospective non‐randomised clinical research study according to a protocol approved by the local ethics committee. Twenty‐eight consecutive adult patients with a histologic diagnosis of malignant melanoma with Breslow thickness greater than 1.0 mm (AJCC stage T2‐4N0M0), who underwent SLB within 10 days following ^99mTc‐MIBI scanning were included. Criteria for exclusion were as follows: clinical evidence of regional lymph node metastases or distant metastatic (M1) disease; palpable lymphadenopathy; infection or inflammation in the regional node basin(s); prior surgery to the draining basin; prior wide local excision (greater than 1.0 cm margin) of primary lesion; pregnancy or breast feeding; and history of prior malignancy. Informed consent was obtained from all patients.

Pre‐study staging

Minimum pre‐study staging evaluation included a complete history and physical examination, liver function tests, serum alkaline phosphatase and lactate dehydrogenase levels, and chest radiograph to screen for metastatic disease. Abnormal findings were further investigated with conventional diagnostic imaging before entry into the study. Subjects with confirmed regional or distant metastatic disease were ineligible.

^99mTc‐MIBI scintigraphy

^99mTc‐MIBI scanning was performed within 7 days of eligibility confirmation, acquiring images 10 min after the intravenous injection of 740‐1110 MBq. The radiopharmaceutical was injected in an antecubital vein or dorsal pedis vein, depending on the topography of primary lesion, in order to avoid non‐specific accidental tracer accumulation in regional lymph nodes due to extravasation at injection site. The equipment consisted of a large‐field‐of‐view rectangular gamma camera (Sophy DSX, Sopha Medical, Buc, France) fitted with a low energy, high resolution collimator. Planar images of regional lymph nodes were acquired on 256 × 256 matrix, using a 10% window centered on an energy peak of 140 keV. We used an isotime acquisition of 10 min for each view. The following regions were scanned depending on the primary lesion‘s location: head and neck (anterior and lateral views with extended neck), axillary regions (anterior thoracic view with arms raised behind the head), and inguinal regions (anterior pelvic view). A lesion was defined as a focus of increased MIBI uptake in a lymph node basin compared with the intensity of surrounding activity. The skin covering such focus was marked with an indelible marker with the help of a ⁵⁷Co penmarker.

Sentinel node biopsy

Preoperative Lymphoscintigraphy

Lymphoscintigraphy was performed 16‐18 hours before surgery. A dose of 111‐185 MBq of Tc‐99m colloidal (Re) sulphide (Nanocis, CIS bio international, Gif‐Sur‐Yvette, France) divided into four insulin syringes (23‐gauge) was intradermally injected (0.1 to 0.3 ml per syringe) around the primary lesion to identify lymphatic basins at risk for metastatic disease and to identify the location of the sentinel node in relation to the rest of the lymphatic basin to direct the surgical incision. Massage and compression of the sites of injection for 1 to 2 minutes were applied to stimulate the lymphatic flow. Scanning of regional lymph nodes was immediately performed in the same camera using 5‐minute consecutive planar images. The position of the nodes was checked with a hand‐held gamma probe (Gammed II, Eurorad, Strasbourg, France) and marked with an intradermal tattoo using a ⁵⁷Co penmarker. We considered a sentinel node as any lymph node receiving direct lymphatic drainage from a lesion site [18].

Intraoperative Lymphatic Mapping

All basins identified by lymphoscintigraphy were explored through incisions directed by the use of a gamma probe. Radioactivity (in counts\sec) of the sentinel node(s) and the adjacent tissues was measured in vivo and verified ex vivo after removal. A signal to background ratio higher than 2 to 3 in vivo and higher than 10 ex vivo was considered significant. If radioactivity levels comparable with that detected in the suspected sentinel node were found in other nodes, then these were also excised. The use of blue dye was left at discretion of the surgeon.

Histological Analysis of the Sentinel Nodes

Serial sections of 1.0 mm of the sentinel node(s) were examined by the pathologist using conventional techniques (hematoxylin and eosin). Sentinel nodes negative for metastases by this analysis were recut for additional sections and stained with S‐100 and HMB‐45 immuno‐stains.

Statistical Analysis

Scintigraphic findings for each node basin at risk were co‐registered and compared with histologic analysis of SNB tissue from the same basin and also to clinical follow‐up examination. The results of ^99mTc‐MIBI scintigraphy were expressed in terms of sensitivity, specificity, positive and negative predictive values. Estimates are presented with a 95% confidence interval (95% CI). The Fisher exact test was used to compare MIBI results in different sub‐samples. Group differences were considered significant at P < 0.05.

A focus with abnormal MIBI uptake in the lymphatic basin draining the primary tumour was defined as a metastasis and thus as true‐positive if this was confirmed by histology. Otherwise, all abnormal foci not confirmed as malignant by histology were interpreted as false positive results. A true‐negative result was a case with a normal MIBI scan defined benign by histology of sentinel nodes without evidence of same basin recurrence in a follow‐up period of at least 12 months. Conversely, the result of ^99mTc‐MIBI scan was considered as falsely negative when the sentinel node was histologically involved.

Follow‐up

Each patient was individually followed with a mean follow‐up time of 22 months (range: 12 to 42 months). Post‐therapy surveillance included complete physical examination at the control visits and oriented conventional imaging procedures when clinically indicated. All cases were managed by a multidisciplinary melanoma group study including oncologists, surgeons, dermatologists, nuclear physicians and pathologists.

Results

The patient population included 17 women and 11 men with an age range of 25 to 82 years and a mean age of 55 years. All patients had primary skin melanoma (AJCC pT2‐pT4) with Breslow depths between 1.1 and 9.0 mm (mean, 2.9 mm), 20 lesions being thicker than 1.5 mm (71%).The location of primary melanomas together with the corresponding AJCC stage, scan and SNB results are listed on Table I.

Discussion

SNB has been adopted as the preferred method of nodal staging for melanoma in various major medical centers worldwide, being considered as standard of care by the World Health Organization [19]. The procedure provides with high accuracy valuable prognostic information and has the ability to select patients for therapies such as therapeutic lymphadenectomy, adjuvant treatment with interferon alfa‐2b or immunotherapy [4,20]. However, some authors argued that unless the use of SNB can be shown to improve overall survival, it should only be performed in the context of a clinical trial [20]. Besides, the technique has the disadvantage of being an invasive surgical procedure with documented complications [21,22].

In the present study SNB demonstrated a sensitivity of 100% compared with clinical follow‐up at a mean follow‐up duration of 22 months. No patient with negative SNB developed nodal recurrence during the study. However, a false‐negative rate of 9% to 11% for this procedure has been reported in the literature [23,24]. This disagreement is likely to be due to the relatively short length of the follow‐up period for this study.

Initial reports suggest that ^99mTc‐MIBI scintigraphy is an accurate technique for the detection of recurrent melanoma lesions [13‐15, 25]. In a series with 82 patients studied during post‐surgical follow‐up, ^99mTc‐MIBI scanning demonstrated a sensitivity of 92% and a specificity of 96% for the detection of metastatic lesions [14]. However, 35% of patients presented clinically or radiologically evident recurrent disease at the time of ^99mTc‐MIBI imaging. In 14 patients the procedure detected previously unknown metastatic lesions including nodal metastases. Recently, Augusseau‐Caillot et al. [16], reported a sensitivity of 95% and a specificity of 85% for the detection of nodal metastases in a series of 37 patients with clinically questionable lymph nodes around lymphatic basins of previously surgically treated melanomas.

The present study is the first to comprehensively evaluate staging of regional lymph node basins by means of ^99mTc‐MIBI scintigraphy in a homogeneous group of patients with melanoma clinically localized to the skin. The technique resulted in overall sensitivity and specificity of 83% and 93% respectively for the detection of regional lymph node metastases in a sample with nodal disease prevalence of 44%. In our study, the percentage of positive SNBs was higher than those reported in larger series (18%‐23%), [26, 27]. Since tumour thickness is a well known predictor of occult lymph node metastases in patients with early stage melanoma [28], the high proportion of thick lesions included in the present study (71%), could partially explain the observed prevalence of nodal disease.

From a clinical point of view, ^99mTc‐MIBI scintigraphy appear to have insufficient sensitivity for the evaluation of clinically occult lymph node metastases, with a false negative rate of 17% related to the detection of small deposits of microscopic disease (two false negative results in patients with micrometastatic disease identified by immunostaining alone). The limited spatial resolution of the gamma camera (9.0 mm) is certainly the main reason explaining the inability of ^99mTc‐MIBI scintigraphy to detect micrometastases in sentinel nodes of patients with early stage melanoma. Therefore, the technique cannot replace surgical staging of regional lymph node basins. It could be possible that ^99mTc‐MIBI imaging may have a secondary role in staging of regional lymph nodes in patients who are not good candidates for SNB, such as those who have had prior wide local excision, flaps, or grafts that may interfere with lymphatic drainage from the primary lesion, rendering SNB less reliable. Nevertheless, since patients with those characteristics were excluded from the present study, the validity of such a hypothesis needs to be proved in the framework of an appropriate trial design.

We also performed subset analyses in order to identify a subgroup of patients more likely to have successful imaging of occult regional lymph node metastases by ^99mTc‐MIBI. Certain high‐risk populations, such as patients with thick primary lesions may demonstrate better performance with ^99mTc‐MIBI imaging for regional nodal metastases. Subset analysis by Breslow thickness, considering a cut‐off point of 2.1 mm, showed a trend toward better ^99mTc‐MIBI sensitivity for detection of occult N1 disease for the group of patients with thicker lesions (> 2.1 mm). Interestingly, it has been shown recently that sentinel node status holds important prognostic information in patients with lesions thicker than 4.0 mm [29,30].

Recent studies underlined the low efficiency of PET for diagnosing subclinical nodal involvement, with sensitivities ranging from 0 to 17% [9, 10, 12]. Nevertheless, authors included patient samples with a nodal disease prevalence of 24%‐28%, which is far below the value observed in the present study (44%). This fact could be related to a higher burden of regional lymph node disease in our sample. Therefore, in order to compare the diagnostic accuracy of MIBI scanning and FDG PET, it is necessary to design a clinical trial, performing both techniques in matched populations. Besides, the limited availability of cyclotron production and PET scanners in certain countries are significant disadvantages of such techniques.

The mechanisms involved in ^99mTc‐MIBI uptake in tumour cells are probably related to intracellular retention of the tracer due to strongly negative potentials across the membrane bilayers secondary to increased metabolic requirements of these cells [31, 32]. Furthermore, this radiopharmaceutical has been validated as a transport substrate of P‐glycoprotein and the multidrug resistance‐associated protein (MRP1), which are ATP‐dependent efflux pumps [33]. Therefore, it could be assumed that the low expression of both proteins observed on plasma membranes from melanoma cells could also contribute to the tumour retention of this tracer [34, 35].

Conclusions

^99mTc‐MIBI is a readily available radiopharmaceutical and the imaging procedure can be performed using current nuclear equipment. The procedure appears insufficiently sensitive for localizing microscopic sentinel node metastases in patients with intermediate‐high risk clinically localized melanoma, SNB being the procedure of choice for such evaluation. The clinical value of MIBI imaging in patients who are not good candidates for SNB needs to be tested in appropriate clinical settings. Acknowledgements. This work was supported by a research grant from the Comisión Sectorial de Investigación Científica (C.S.I.C.), University of Uruguay; from the Comisión Honoraria de Lucha Contra el Cáncer (C.H.L.C.C.), Montevideo, Uruguay; and from the International Atomic Energy Agency (I.A.E.A.),Vienna, Austria.

1 . Rigel DS, Carucci JA. Malignant melanoma: Prevention, early detection, and treatment in the 21^st century. CA Cancer J Clin 2000; 50: 215‐36.

2 . Chao C, McMasters KM. Update on the use of sentinel node biopsy in patients with melanoma: who and how. Curr Opin Oncol 2002; 14: 217‐20.

3 . Morton DL, Wen DR, Wong JH, et al. Technical details of intraoperative lymphatic mapping for early stage melanoma. Arch Surg 1992; 127: 392‐9.

4 . Dubois RW, Swetter SM, Atkins M, et al. Developing indications for the use of sentinel lymph node biopsy and adjuvant high‐dose interferon alfa‐2b in melanoma. Arch Dermatol 2001; 137: 1217‐24.

5 . Balch CM, Soong SJ, Gershenwald JE, et al. Prognostic factors analysis of 17,600 melanoma patients: validation of the American Joint Committee on Cancer melanoma staging system. J Clin Oncol 2001; 19: 3622‐34.

6 . Voit C, Schoengen A, Schwurzer‐Voit M, et al. The role of ultrasound in detection and management of regional disease in melanoma patients. Semin Oncol 2002; 29: 353‐60.

7 . Swetter SM, Carroll LA, Johnson DL, Segall GM. Positron emission tomography is superior to computed tomography for metastatic detection in melanoma patients. Ann Surg Oncol 2002; 9: 646‐53.

8 . Stas M, Stroobants S, Dupont P, et al. 18‐FDG PET scan in the staging of recurrent melanoma: additional value and therapeutic impact. Melanoma Res 2002; 12: 479‐90.

9 . Wagner JD, Schauwecker D, Davidson D, et al. Prospective study of fluorodeoxyglucose‐positron Emission tomography imaging of lymph node basins in melanoma patients undergoing sentinel node biopsy. J Clin Oncol 1999; 17: 1508‐15.

10 . Acland KM, Healy C, Calonje E, et al. Comparison of positron emission tomography scanning and sentinel node biopsy in the detection of micrometastases of primary cutaneous malignant melanoma. J Clin Oncol 2001; 19: 2674‐8.

11 . Kokoska MS, Olson G, Kelemen PR, et al. The use of lymphoscintigraphy and PET in the management of head and neck melanoma. Otolaryngol Head Neck Surg 2001; 125: 213‐20.

12 . Belhocine T, Pierard G, De Labrassinne M, et al. Staging of regional nodes in AJCC stage I and II melanoma: ¹⁸ FDG PET imaging versus sentinel node detection. The Oncologist 2002; 7: 271‐8.

13 . Alonso O, Martínez M, Mut F, et al. Detection of recurrent malignant melanoma with ^99m Tc‐MIBI scintigraphy. Melanoma Res 1998; 8: 355‐60.

14 . Alonso O, Mut F, Martínez M, et al. Evaluación centellográfica con ^99m Tc‐MIBI en pacientes con melanoma. Alasbimn Journal 1998. Available at:

http:\\www.alasbimnjournal.cl\revistas\1\melanoma.htm.

Accessed March 6, 2003.

15 . Soler C, Perrot JL, Thiffet O, et al. The role of technetium‐99m sestamibi single photon emission tomography in the follow‐up of malignant melanoma and the detection of lymph node metastases. Eur J Nucl Med 1997; 24: 1522‐5.

16 . Augusseau‐Caillot A, Soler C, Teyssier F, et al. Interest of PS100 assay when 99mTc sestamibi scintigraphy failed to identify lymph node metastases of melanoma. Eur J Dermatol 2001; 11: 432‐5.

17 . Balch CM, Buzaid AC, Soong SJ, et al Final version of the American Joint Committee on Cancer staging system for cutaneous melanoma. J Clin Oncol 2001; 19: 3635‐48.

18 . Thompson JF, Hunt JA, Culjak G, et al. Popliteal lymph node metastasis from primary cutaneous melanoma. Eur J Surg Oncol 2000; 26: 172‐6.

19 . WHO declares lymphatic mapping to be the standard of care for melanoma. Oncology 1999; 13: 288.

20 . McMasters KM, Reintgen DS, Ross MI, et al. Sentinel lymph node biopsy for melanoma: Controversy despite widespread agreement. J Clin Oncol 2001; 19: 2851‐5.

21 . Wrone DA, Tanabe KK, Cosimi AB, et al. Lymphedema after sentinel lymph node biopsy for cutaneous melanoma: A report of 5 cases. Arch Dermatol 2000; 136: 511‐4.

22 . Cimmino VM, Brown AC, Szocik JF, et al. Allergic reactions to isosulfan blue during sentinel node biopsy‐‐a common event. Surgery 2001; 130: 439‐42.

23 . Vuylsteke RJ, van Leeuwen PA, Muller MG, et al. Clinical outcome of stage I\II melanoma patients after selective sentinel lymph node dissection: long‐term follow‐up results. J Clin Oncol 2003; 21: 1057‐65.

24 . Jansen L, Nieweg OE, Peterse JL, et al. Reliability of sentinel lymph node biopsy for staging melanoma. Br J Surg 2000; 87: 484‐9.

25 . Martínez MA, Alonso O, Delgado LB, et al. Cutaneous malignant melanoma: scintigraphic detection of recurrent disease with Tc‐99m MIBI. Eur J Dermatol 1997; 7: 433‐5.

26 . Morton DL, Thompson JF, Essner R, et al. Validation of the accuracy of intraoperative lymphatic mapping and sentinel lymphadenectomy for early‐stage melanoma. A multicenter trial. Ann Surg 1999; 230: 453‐65.

27 . Cascinelli N, Belli F, Santinami M, et al. Sentinel lymph node biopsy in cutaneous melanoma: the WHO Melanoma Program experience. Ann Surg Oncol 2000; 7: 469‐74.

28 . Lens MB, Dawes M, Newton‐Bishop JA, Goodacre T. Tumour thickness as a predictor of occult lymph node metastases in patients with stage I and II melanoma undergoing sentinel lymph node biopsy. Br J Surg 2002; 89: 1223‐7.

29 . Essner R, Chung MH, Bleicher R, et al. Prognostic implications of thick (> ∓ 4‐mm) melanoma in the era of intraoperative lymphatic mapping and sentinel lymphadenectomy. Ann Surg Oncol 2002; 9: 754‐61.

30 . Thompson JF, Shaw H. The prognosis of patients with thick primary melanomas: Is regional lymph node status relevant, and does removing positive regional nodes influence outcome ¿ Ann Surg Oncol 2002; 9: 719‐22.

31 . Piwnica‐Worms D, Kronauge JF, Chiu ML. Uptake and retention of hexakis (2‐methoxyisobutylisonitrile) technetium (I): mitochondrial plasma membrane potential dependence. Circulation 1990; 82: 1826‐38.

32 . Chen LB. Mitochondrial membrane potentials in lung cells. Annu Rev Cell Biol 1988; 4: 155‐81.

33 . Tan B, Piwnica‐Worms D, Ratner L. Multidrug resistance transporters and modulation. Curr Opin Oncol 2000; 12: 450‐8.

34 . Molinari A, Calcabrini A, Meschini S, et al. Detection of P‐glycoprotein in the Golgi apparatus of drug‐untreated human melanoma cells. Int J Cancer 1998; 75: 885‐93.

35 . Helmbach H, Sinha P, Schadendorf D. Human melanoma: drug resistance. Recent Results Cancer Res 2003; 161: 93‐110.