Positron emission tomography scanning in malignant melanoma

Clinical role of FDG PET in evaluation of cancer patients

Positron emission tomography (PET) is a diagnostic imaging technique that allows identification of biochemical and physiologic alterations in tumors. Use of PET performed with 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG) significantly improves the accuracy of tumor imaging. In terms of oncologic applications, FDG PET has already gained widespread acceptance in the initial staging of cancer, management of recurrent cancer, and monitoring the response to therapy. With conventional imaging modalities, size criteria are used to distinguish between benign and malignant disease in lymph nodes; conversely, FDG PET is based on identification of fundamental aspects of tumor metabolism. FDG uptake in tumors is proportional to the metabolic rate of viable tumor cells, which have an increased demand for glucose. The high sensitivity and high negative predictive value of FDG PET in most malignant tumors enable this technique to play an even greater role in tumor management at initial staging and follow-up.

Melanoma patients evaluated by four different positron emission tomography reconstruction techniques

One hundred and nineteen patients with malignant melanoma were studied using 2-[ F]-fluoro-2-deoxy-D-glucose positron emission tomography (FDG PET). The images were reconstructed using ordered subset expectation maximization with and without attenuation correction and filtered backprojection with and without attenuation correction. The most probable draining lymph node chains were surgically explored and the tumour volume was quantified at histology. The four different reconstructions of the PET images were retrospectively graded on a five-point scale by two blind readers and compared with the tumour volume. The readers agreed within +/-1 grade 93% (529/568) of the time. Comparing the areas under the receiver operating characteristic (ROC) curves gave 0.698, 0.668, 0.694 and 0.684 for the four reconstruction techniques. The lowest value comparing any pair of the four reconstruction techniques was P=0.371. Thus, none of the reconstruction techniques gave significantly better results than any of the others. The sensitivity of detection was 85% for tumour volumes of 113 m or more (about 6 mm in diameter), but only 4% for tumours less than this size. It can be concluded that the use of attenuation correction gives aesthetically more pleasing images, but the sensitivity and specificity are not significantly improved.

New diagnostic techniques in staging in the surgical treatment of cutaneous malignant melanoma

The emphasis of the research on the surgical treatment of melanoma has been on the resection margins, the role of elective lymph node dissection in high risk patients and the value of adjuvant regional treatment with hyperthermic isolated lymph perfusion with melphalan. Parallel to this research, new diagnostic techniques, such as Positron Emission Tomography and the introduction of the sentinel lymph node biopsy with advanced laboratory methods such as immuno-histochemical markers, and reverse transcriptase polymerase chain reaction, have been developed to facilitate early detection of metastatic melanoma. The role of these new techniques on the staging and surgical treatment of melanoma is discussed in this paper.

Staging of regional nodes in AJCC stage I and II melanoma: 18FDG PET imaging versus sentinel node detection

PRIMARY PURPOSE

The staging of regional nodes by means of sentinel node detection has been shown to accurately detect subclinical nodal metastases from cutaneous melanoma. On the other hand, the oncological applications of 18F-fluoro-2-deoxy-D-glucose positron emission tomography (18FDG PET) are, nowadays, firmly established. However, the sensitivity of such metabolic imaging for staging the regional nodes in primary melanoma remains debatable. We prospectively assessed the actual value of PET for detecting sentinel node metastases in 21 consecutive patients presenting with early-stage melanoma.

MATERIALS AND METHODS

Twenty-one melanoma patients scheduled for lymphatic mapping and sentinel lymphadenectomy underwent fully corrected whole-body PET using 18FDG. In all cases, the disease was initially classified as either stage I or II, from the latest version of the American Joint Committee on Cancer staging system. The sentinel node detection was systematically performed within the week following the PET scan. Serial sections of the sentinel nodes were analyzed by both conventional pathology and immunohistochemical staining. Metastatic sentinel nodes were also assessed for the size of tumor deposits and the degree of nodal involvement (focal, partial, or massive). The median follow-up time was 12 months.

RESULTS

Six of the 21 patients (28.5%) had an involved sentinel node. PET was positive in only one case with a sentinel node >1 cm. In the five other cases, the sentinel nodes missed by PET were <1 cm with focal and/or partial involvements. One patient, free of regional nodal metastases in both sentinel node detection and PET imaging, had, however, a same-basin recurrence 3 months later. In another case, PET had one false positive result. Overall, the sentinel detection of subclinical nodal metastases had a sensitivity of 86%. PET detected only 14% of sentinel node metastases.

CONCLUSIONS

Sentinel node detection remains the procedure of choice for detecting subclinical lymph node involvement from primary cutaneous melanoma. Owing to its limited spatial resolution, PET appears insufficiently sensitive to identify microscopic nodal metastases. As a practical consequence, metabolic imaging is not recommended as a first-line imaging strategy for staging regional lymph nodes in patients with stage I or II melanoma.

Current concepts in the management of patients with melanoma

Melanoma is a significant health problem. Despite public education and free cancer screenings, the incidence and mortality of melanoma continues to rise; however, many currently diagnosed melanomas are thin lesions, suggesting that education and awareness is having an impact. In addition, there are still subsets of patients who need increased surveillance in order to increase their survival. Although large congenital nevi may be precursors of melanoma, small and medium congenital nevi have an insignificant risk for melanoma development. Large congenital nevi, which are axial in location, appear to be more likely to develop melanoma and are associated with melanocytosis and melanoma of the CNS, both of which portend a poor prognosis. Recently, the recommended margins of excision have become more conservative so that many of the surgical defects can be closed primarily. Lymphoscintigraphy and sentinel node biopsy have replaced elective node dissections, thus decreasing the morbidity associated with the surgical management of melanoma. Although controversy still exists as to whether or not sentinel lymph node biopsy alters a patient's prognosis, it has been shown to be a powerful prognostic indicator. Although most melanomas are managed by routine surgical excision, other modalities are sometimes employed. For example, cryosurgery or radiation therapy may be indicated in the frail, elderly individual with a large facial lentigo maligna. Mohs surgery is the treatment of choice for head and neck melanomas and those located in areas where maximum preservation of tissue is required and for desmoplastic and acral lentiginous melanomas. Much more work remains in the area of adjuvant therapy, chemotherapy, and immunotherapy. Dacarbazine remains the drug of choice in disseminated melanoma, but remissions are usually short lived. Interleukin and biochemotherapy has yielded good results but the percentage benefiting is small. Although high dose interferon increases disease-free and overall survival in some patients, it remains a controversial drug which is not easily tolerated. In the new staging system for melanoma, ulceration is second only to Breslow's thickness. In transit (satellite) lesions have also been included in this new system. The new system also recognizes that patients with only microscopic metastatic nodal disease fare better than patients with clinically enlarged metastatic nodes and that it is the number of nodes involved with metastases, not their size, that determines the patient's prognosis. Except for lesions <1mm thick, the Clark's level of invasion has been de-emphasized.

18-FDG PET scan in the staging of recurrent melanoma: additional value and therapeutic impact

Staging of melanoma patients by means of whole body functional imaging in a single evaluation session using positron emission tomography (PET) with fluorine-18- labelled deoxy-d-glucose (FDG) as a metabolic tracer has created much interest over the last decade. After enthusiastic pilot studies, more attention has been paid to the false-negative and false-positive results of this technique than to its true therapeutic impact. This study aimed to evaluate (1) the sensitivity and specificity of this technique at a single lesion level compared with conventional screening procedures (CSP) - both of these accompanied by careful clinical examination; and (2) the additional value of the PET scan at the level of the individual patient and its therapeutic impact for different types of melanoma recurrence. A consecutive series of 100 PET scans performed on 84 melanoma patients with regional or distant recurrence according to CSP (89 PET scans) or suspicion of recurrence, i.e. inconclusive CSP (11 PET scans), were retrospectively analysed and compared with the CSP results. At the single lesion level, PET scan and CSP showed a sensitivity of 85 and 81%, a specificity of 90 and 87% and an accuracy of 88 and 84%, respectively. PET provided false-negative results for small skin metastases and brain involvement; false-positive results were associated with unrelated benign or malignant tumours and peripheral soft tissue and bone uptake. PET scan showed an additional value over and above CSP at the individual patient's level by true upstaging in 10 cases, true downstaging in 24 cases and depiction of more lesions within the same stage of disease in 15 cases. The overall therapeutic impact reached 26%: 17 out of 71 (24%) cases with regional recurrence, one out of 18 cases (5.5%) with distant metastasis and eight out of 11 cases (73%) with suspicion of recurrence where CSP remained doubtful. However, in 19 cases comparison between CSP and PET resulted in discordant findings, suggesting upstaging in one area and downstaging at another site within the same patient. In conclusion, PET scan has an additional value in the staging of recurrent melanoma, providing it is accompanied by careful clinical examination and specific brain imaging. However, in the absence of evidence of metastasis or unrelated conditions at the same site on CSP, PET spots may represent false-positive images, which would falsely upgrade a patient to an incurable state, or they may be early true-positive findings, which will become evident during close follow-up.

Positron emission tomography is superior to computed tomography for metastatic detection in melanoma patients

BACKGROUND

Whole-body positron emission tomography (PET) provides diagnostic information not currently available with traditional imaging and may improve the accuracy of staging melanoma patients.

METHODS

A retrospective cohort review was performed of 104 patients with primary or recurrent melanoma who underwent PET to determine sensitivity/specificity for metastatic detection compared with body computed tomography (CT). One hundred fifty-seven PET and 70 CT scans were analyzed, with a median patient follow-up of 24 months. Metastases were confirmed with positive histology (87.5%) or documented disease progression (12.5%). Fifty-three patients prospectively underwent consecutive studies within a mean 3-week interval for direct comparative analysis.

RESULTS

PET demonstrated 84% sensitivity (95% confidence interval [CI],.78 to.89) and 97% specificity (95% CI,.91 to.99), whereas CT showed 58% sensitivity (95% CI,.49 to.66) and 70% specificity (95% CI,.51 to.84). Exclusion of areas not evaluated on CT (head, neck/supraclavicular, extremities) increased CT sensitivity to 69% (95% CI,.59 to.77). Sixty-six consecutive PET and CT scans were performed with 81% and 57% of metastases detected, respectively.

CONCLUSIONS

PET is more sensitive and specific than CT for detection of melanoma metastasis and should be considered the primary staging study for recurrent disease. PET shows greater ability to detect soft tissue, small-bowel, and lymph node metastasis that do not meet criteria designated as abnormal by CT. PET is superior to CT even when sites not routinely evaluated by CT are excluded from comparative analysis.

The revised American Joint Committee on Cancer staging system for melanoma

Substantial progress has been made in identifying the most significant clinical and pathologic characteristics of melanoma that predict for metastasis and survival. The American Joint Committee on Cancer (AJCC) staging system for cutaneous melanoma was recently revised to include these prognostic variables. Major changes in the staging include: (1) melanoma thickness and ulceration but not level of invasion will be used in the T category (except for T1 melanomas); (2) the number of metastatic lymph nodes rather than their gross dimensions and the delineation of clinically occult (ie, "microscopic") versus clinically apparent (ie, "macroscopic") nodal metastases will be used in the N category; (3) the site of distant metastases and the presence of elevated serum lactate dehydrogenase (LDH) will be used in the M category; (4) all patients with stage I, II, or III disease will be upstaged when a primary melanoma is ulcerated; (5) satellite metastases around a primary melanoma and in-transit metastases will be merged into a single staging entity that is grouped into stage III disease; and (6) distinct definitions for clinical and pathologic staging will take into account the new staging information gained from intraoperative lymphatic mapping and sentinel node biopsy.

Lymphatic mapping in solid neoplasms: state of the art

BACKGROUND

Lymphatic mapping and sentinel lymph node biopsy is an established technique for the staging and treatment of melanoma. The success of lymphatic mapping in this realm has broadened its application to other solid neoplasms. This update reviews the status of sentinel lymph node biopsy in its most widely cited applications.

METHODS

Seminal manuscripts on lymphatic mapping in melanoma, breast, colon, vulvar, cervical, lung, gastric, and head and neck cancers are reviewed.

RESULTS

Studies suggest that the application of lymphatic mapping as a staging tool in breast cancer and melanoma is justified when applied by trained surgeons. Additional validation is necessary before sentinel node biopsy is advocated in gynecologic, colon, lung, and head and neck cancer.

CONCLUSIONS

As in breast cancer and melanoma, validation of the sentinel node concept in other solid tumors must occur in institutions other than those in which the technique is being developed before it is generally applied to other neoplasms.

Reproducibility and clinical value of 18F-fluorodeoxyglucose positron emission tomography in recurrent melanoma

The purpose of this study was to assess the reproducibility and clinical impact of positron emission tomography (PET) with 18F-fluorodeoxyglucose (FDG) in patients with (suspected) recurrent melanoma. The clinical value of PET was prospectively measured in 58 consecutive patients referred for PET because of unresolved clinical questions after conventional work-up. Diagnostic understanding and therapy choice by referring physicians were evaluated before, directly after, and 6 months after PET. Observer agreement of PET readings was measured with respect to various parameters (interpretation, number and localization of lesions, 'clinically decisive' metastases), using intra-class correlation coefficients. FDG PET improved diagnostic understanding in 33 cases (57%). In six patients (10%), diagnostic understanding was solely based on PET information. According to the attending clinicians, PET contributed to a positive change of planned treatment in 23 patients (40%) and increased confidence in the chosen treatment in 23 (40%). Observer agreement of PET readings was very high (intra-class correlation coefficients were between 0.87 and 0.94). The diagnostic value related especially to the whole-body scan technique and the superior specificity, compared to conventional work-up. It is concluded that, in problematical cases with (suspected) recurrent melanoma, 18F-FDG PET had considerable impact on diagnostic understanding and management. Together with the excellent observer reliability, these results justify further studies to determine the optimal place of PET in routine diagnostic algorithms in recurrent melanoma.

Positron emission tomography for staging and management of malignant melanoma

BACKGROUND

The incidence of malignant melanoma is rising; it now has an incidence of ten per 100 000 per annum in the UK. The development of metastases is unpredictable, but prognosis is linked directly to the initial stage at diagnosis. Positron emission tomography (PET) can allow the detection of malignant cells at a relatively early stage.

METHODS

A review of the literature was undertaken by searching the Medline database for the period 1980-2000 without any language restrictions.

RESULTS

The overall sensitivity and specificity of PET are 74-100 and 67-100 per cent respectively. PET has a reduced sensitivity and specificity for thinner lesions (less than 1 x 5 mm). Comparison with computed tomography and magnetic resonance imaging has shown a higher sensitivity and specificity for PET in all regions of the body except the thorax.

CONCLUSION

Currently the accepted indication for PET is recurrent melanoma when surgical intervention is being considered. However, other potential indications include the detection of occult or distant metastasis at initial presentation and the clarification of abnormal radiological findings at follow-up. The routine use of PET for American Joint Commission on Cancer stage I or II disease is of uncertain benefit and is not indicated at present.

A shifting landscape: what will be next FDG in PET oncology?

The tumor-seeking agent most widely used in positron emission tomography (PET) is 2-(18)F-fluorodeoxy-D-glucose (FDG). The clinical usefulness of FDG PET has already been proved in detecting, staging and restaging various kinds of malignant tumors, but nuclear medicine physicians suffer from a "diagnostic dilemma," in which a relatively high false positive ratio of FDG PET in diagnosing malignant tumors prevails. To increase more specific tumor uptake or more specific tumor characterization, numerous PET radiopharmaceuticals have been developed, and some of them are being tested in clinical trials. This review will briefly survey the tumor uptake mechanism and clinical significance of representative non-FDG PET radiopharmaceuticals used in clinical trials for patients with cancers.

Whole-body FDG-PET imaging in the management of patients with cancer

Fluorodeoxyglucose-positron emission tomography (FDG-PET) imaging is increasingly used for the management of patients with cancer. The technique is now well accepted by most physicians as an effective complement to the existing imaging modalities. For many malignancies, PET achieves high sensitivity and specificity. The critical role of this powerful technique is realized increasingly in the day-to-day practice of oncology. This is particularly true for the management of patients with non-small-cell lung cancer (NSCLC). The contribution of PET for the selection of patients eligible for curative treatments in this setting is well established. Convincing data also exist to support the use of PET for evaluating patients with recurrent colorectal carcinoma, for staging and restaging lymphomas, and for diagnosing recurrent thyroid carcinoma in the presence of elevated thyroglobulin and negative 131I scans. Other indications include staging of various recurrent malignancies, such as breast cancer, melanoma, and head and neck and gynecologic carcinomas. Existing data are limited for the determination of the impact of PET in certain malignancies, and further studies, which should include outcome information, will allow clarification of the role of this modality for such indications. Despite the small number of studies specifically designed to assess changes in management plans for some malignancies after performing PET the overall favorable results are encouraging enough at this time to include this modality as an essential element of the practice of modern oncology. Finally, the evolving role of PET imaging as a predictor of response after local or systemic treatment may add a major dimension to the application of this novel technique.

FDG-PET sensitivity for melanoma lymph node metastases is dependent on tumor volume

BACKGROUND AND OBJECTIVES

The purpose of this study is to determine the tumor volume threshold for successful positron emission tomography (PET) imaging of melanoma nodal metastases.

METHODS

Review of a clinical series of patients who had FDG-PET imaging of regional lymph node basins followed by lymphadenectomy. Lymph node tumor volumes were calculated from direct measurements of metastatic nodule(s) in formalin fixed specimens. PET scan interpretations were correlated with histology to determine sensitivity. Sensitivity was correlated with the aggregate lymph node tumor volume in the nodal basin and with AJCC stage group.

RESULTS

Forty-five patients with 49 pathologically positive regional nodal basins comprised the study group. Median total basin tumor volume was 28.3 mm(3)(range 0.004-22,879 mm(3)). FDG-PET sensitivity for detection of all tumor volumes was 0.49. The observed 90% sensitivity threshold for detection of nodal metastases was > or = 78 mm(3). PET sensitivity was 0.14 for detection of tumor volumes < 78 mm(3). PET sensitivity differed by prescan AJCC stage: I-0.0; II-0.24; III-0.81; IV-1.0 (P < 0.001).

CONCLUSIONS

FDG-PET reliably detects lymph node tumor deposits greater than approximately 80 mm(3) volume, but sensitivity falls rapidly below this. This amount of tumor is most likely to occur in patients with AJCC stage III or IV disease.

Clinical role of positron emission tomography in oncology

Positron emission tomography (PET) is now in routine use in oncology, through the success of metabolic imaging, mainly with fluorodeoxyglucose (FDG). Clear benefit is obtained with FDG PET in the assessment of patients with recurrent or residual disease, especially colorectal cancer and lymphoma. Preoperative staging of non-small-cell lung cancer with FDG PET is of proven benefit. Staging and restaging of patients with melanoma of stage II or greater is useful, and FDG PET has also been successfully used to investigate single pulmonary nodules. Tumour grading has been assessed, especially in the brain, but an important and emerging indication is the evaluation of tumour response with PET. Rapid decline of FDG uptake has been observed in responsive cancers. Further advances are being made with other fluorine-18-labelled and generator-based PET tracers, the only ones that can be used in units without dedicated cyclotrons.