Clinical Value of PET/CT in Staging Melanoma and Potential New Radiotracers

Diagnostic value of 18 F-fluoro-2-deoxyglucose positron emission tomography/computed tomography imaging in acral melanoma-predominant Asian patients

BACKGROUND

Tumor staging is crucial for melanoma, of which acral melanoma is the predominant subtype in Asians. 18 F-fluoro-2-deoxyglucose (FDG) positron emission tomography (PET) and 18 F-FDG-PET/computed tomography ( 18 F-FDG-PET/CT) serve as noninvasive imaging tools for tumor staging. However, the literature is scarce on the diagnostic value of PET for acral melanoma.

METHODS

From January 1, 2006 to November 30, 2022, a total of 352 patients were diagnosed with melanoma at our hospital. Of them, 90 were diagnosed with cutaneous melanoma and underwent preoperative PET/CT for staging and sentinel lymph node biopsy or complete lymph node dissection. Staging of PET/CT was confirmed by histopathology or following imaging. The lymph node biopsy, distant metastasis status, and PET/CT imaging results were analyzed.

RESULTS

Of all the 90 patients with cutaneous melanoma, 72 of them were diagnosed as acral melanoma (80.0%). Compared with the histopathologic results, the lymph nodes were true-positive, true-negative, false-positive, and false-negative in 12, 54, 7, and 17 cases, respectively. The sensitivity of PET/CT for local lymph nodes was 41.4% (95% CI, 23.5%-61.1%), whereas its specificity was 88.5% (95% CI, 77.8%-95.3%). As for the detection of distal metastasis, the PET results were true-positive, true-negative, false-positive, and false-negative in 6, 65, 15, and 4 cases, respectively. The sensitivity of PET for distal metastasis detection was 60.0% (95% CI, 26.2%-87.8%), whereas its specificity was 81.3% (95% CI, 71.0%-89.1%).

CONCLUSION

Although noninvasive, PET/CT has relatively low sensitivity in regional lymph node evaluations, and fair sensitivity in distal metastasis detection in Asian patients with acral melanoma. Thus, PET/CT may be more useful in patients with clinically palpable nodes or more advanced disease stages.

Uveal Melanoma Metastasis to the Thyroid

Background

Around 1.2 to 3.1% of thyroid malignancies are due to metastasis. Among them, cutaneous malignant melanomas constitute 4% of malignancy metastasized to the thyroid. Uveal melanoma is uncommon, and its metastasis to the thyroid has only rarely been reported. Hereby, we describe an unusual case of uveal melanoma metastasized to the thyroid and discuss the concept of correct diagnosis. Case Report. During a routine ophthalmological examination, an 86-year-old Caucasian female was found to have retinal detachment secondary to choroidal melanoma. She was treated with gamma knife which resulted in reduction of tumor size. Three months later, she was noted to have a goiter on physical examination. Follow-up thyroid ultrasonography demonstrated numerous vascularized nodules in both lobes. The fine needle aspiration (FNA) of the left dominant nodule was indeterminate the first time and nondiagnostic the second time. FNA of the right dominant nodule was nondiagnostic twice but showed malignant cells the third time. Subsequent immunohistochemistry staining of the FNA sample from the right thyroid nodule confirmed a profile consistent with malignant melanoma.

Conclusion

It should be kept in mind that a thyroid nodule detected in a patient with a diagnosis of uveal melanoma can be metastasis and that uveal melanoma diagnosis should be taken into account for the examination of the thyroid tumors of these patients. It is important to employ immunohistochemical staining FNA examination of the patient with such tumors for markers associated with a patient's known malignancy to facilitate diagnosis.

18F-5-FPN: A Specific Probe for Monitoring Photothermal Therapy Response in Malignant Melanoma

Previously, we successfully synthesized a ¹⁸F-labeled positron-emission tomography (PET) tracer, termed ¹⁸F-5-fluoro-N-(2-[diethylamino]ethyl)picolinamide (¹⁸F-5-FPN), with high specificity for melanin. In this study, we sought to investigate the value of ¹⁸F-5-FPN in assessing the response to photothermal therapy (PTT) in melanoma via comparison with ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) to reveal an early response, recognize early recurrence, and distinguish the inflammatory response during the treatment. B16F10, inflammatory, and MDA-MB-231 models were subjected to ¹⁸F-FDG PET and ¹⁸F-5-FPN PET static acquisitions. We compared quantitative data to assess the specificity of different agents for different diseases. B16F10 and MDA-MB-231subcutaneous tumor models were irradiated with an 808 nm laser for PTT. Their survival was documented to observe the efficacy of and response to PTT, using ¹⁸F-5-FPN and ¹⁸F-FDG PET. ¹⁸F-5-FPN accumulated in B16F10 cell xenografts only, whereas ¹⁸F-FDG accumulated in all three models. Melanin in B16F10 cell xenografts successfully transformed the optical energy into heat. Hematoxylin and eosin (H&E) staining at 24 h revealed destruction and extensive necrosis of tumor tissue. PTT rapidly inhibited the growth of B16F10 cell xenografts and prolonged the median survival. The mean tumor uptakes of ¹⁸F-5-FPN on day 2 (7.52 ± 3.65 %ID/g) and day 6 (10.22 ± 6.00 %ID/g) were much lower than that before treatment (18.33 ± 4.98 %ID/g, p < 0.01). However, a significant difference in ¹⁸F-FDG uptakes was not found between day 1 after PTT and before treatment. Compared with ¹⁸F-FDG, ¹⁸F-5-FPN PET could estimate PTT efficacy in melanoma, monitor minimal recurrence, and distinguish melanoma from inflammation and other carcinoma types, thanks to its high affinity to melanin. ¹⁸F-5-FPN may provide a new approach for precise and accurate evaluation of response, timely management of therapeutic regimens, and sensitive follow-up.

MC1R and melanin-based molecular probes for theranostic of melanoma and beyond

Malignant melanoma is accounting for most of skin cancer-associated mortality. The incidence of melanoma increased every year worldwide especially in western countries. Treatment efficiency is highly related to the stage of melanoma. Therefore, accurate staging and restaging play a pivotal role in the management of melanoma patients. Though 18F-fluorodeoxyglucose (18F-FDG) positron-emission tomography (PET) has been widely used in imaging of tumor metastases, novel radioactive probes for specific targeted imaging of both primary and metastasized melanoma are still desired. Melanocortin receptor 1 (MC1R) and melanin are two promising biomarkers specifically for melanoma, and numerous research groups including us have been actively developing a plethora of radioactive probes based on targeting of MC1R or melanin for over two decades. In this review, some of the MC1R-targeted tracers and melanin-associated molecular imaging probes developed in our research and others have been briefly summarized, and it provides a quick glance of melanoma-targeted probe design and may contribute to further developing novel molecular probes for cancer theranostics.

Clinical Evaluation of an Abbreviated Contrast-Enhanced Whole-Body MRI for Oncologic Follow-Up Imaging

Over the last decades, overall survival for most cancer types has increased due to earlier diagnosis and more effective treatments. Simultaneously, whole-body MRI-(WB-MRI) has gained importance as a radiation free staging alternative to computed tomography. The aim of this study was to evaluate the diagnostic confidence and reproducibility of a novel abbreviated 20-min WB-MRI for oncologic follow-up imaging in patients with melanoma. In total, 24 patients with melanoma were retrospectively included in this institutional review board-approved study. All patients underwent three consecutive staging examinations via WB-MRI in a clinical 3 T MR scanner with an abbreviated 20-min protocol. Three radiologists independently evaluated the images in a blinded, random order regarding image quality (overall image quality, organ-based image quality, sharpness, noise, and artifacts) and regarding its diagnostic confidence on a 5-point-Likert-Scale (5 = excellent). Inter-reader agreement and reproducibility were assessed. Overall image quality and diagnostic confidence were rated to be excellent (median 5, interquartile range [IQR] 5–5). The sharpness of anatomic structures, and the extent of noise and artifacts, as well as the assessment of lymph nodes, liver, bone, and the cutaneous system were rated to be excellent (median 5, IQR 4–5). The image quality of the lung was rated to be good (median 4, IQR 4–5). Therefore, our study demonstrated that the novel accelerated 20-min WB-MRI protocol is feasible, providing high image quality and diagnostic confidence with reliable reproducibility for oncologic follow-up imaging.

Malignancy Rate of Indeterminate Findings on FDG-PET/CT in Cutaneous Melanoma Patients

BACKGROUND

The use of ¹⁸F-2-Fluor-2-desoxy-D-glucose Positron Emission Tomography/Computed Tomography FDG-PET/CT in clinical routine for staging, treatment response monitoring and post treatment surveillance in metastatic melanoma patients has noticeably increased due to significant improvement of the overall survival rate in melanoma patients. However, determining the dignity of the findings with increased metabolic activity on FDG-PET/CT can be sometimes challenging and may need further investigation.

PURPOSE

We aimed to investigate the malignancy rate of indeterminate findings on FDG-PET/CT in metastatic cutaneous melanoma patients.

METHODS

This single-center retrospective study included cutaneous melanoma patients who underwent FDG-PET/CT in clinical routine between 2015 and 2017 with findings reported as indeterminate and therefore requiring further evaluation. The dignity of the included findings was determined by subsequent imaging and, if required, additional histopathology. The impact of the outcome on the clinical management was also reported.

RESULTS

A total of 842 FDG-PET/CT reports of 244 metastatic cutaneous melanoma patients were reviewed. Sixty indeterminate findings were included. Almost half of all indeterminate findings were lymph nodes, lung nodules and cerebral lesions. In total, 43.3% of all included findings proved to be malignant. 81% of all malignant lesions were metastases of cutaneous melanoma, while 19% of all malignant lesions could be attributed to other primary malignancies, such as lung, breast, thyroid and colorectal cancers. Malignant findings influenced clinical management in 60% of the cases.

CONCLUSION

Indeterminate findings on FDG-PET/CT in metastatic cutaneous melanoma patients should be further investigated. Almost one out of every two indeterminate findings on FDG-PET/CT is malignant. The majority of the findings are melanoma manifestations, however, in a significant percentage, other primary tumors are found. Upon verification, patient management is changed in most cases.

A Rare Case of Solitary Pituitary Metastasis From Spitzoid Melanoma Detected by FDG PET/CT

A 33-year-old man had a diagnosis of a spitzoid melanoma by dorsal skin biopsy. During the oncological follow-up, patient underwent whole-body FDG PET/CT for restaging purpose. FDG PET/CT showed a large necrotic mass of the pituitary gland, subsequently confirming a solitary pituitary metastasis from spitzoid melanoma.