Non-Cutaneous Melanoma, Findings and Prognostic Value of FDG PET/CT: A Case Series of 23 patients and review of the literature

Abstract

Objectives: Non-cutaneous malignant melanomas (NCM) are rare malignancies. Due to their nonspecific symptoms, they present later in life. The value of FDG PET/CT in this group of patients is not clear. The aim of this study is to assess the role of FDG PET/CT in the management of NCM and its prognostic implication.

Methods: We retrospectively selected twenty-three patients with a diagnosis of NCM evaluated with FDG PET/CT in Shariati hospital between 2019 and 2021. The PET/CT data were reviewed and compared with available conventional imaging findings. Five patients died within five months. The surviving patients were followed within a time interval of 7 to 27.5 months after their PET/CT study, regarding their disease status.

Results: Among 23 patients (8 ocular, 5 sinonasal, 3 pharyngeal, 2 anorectal, 2 vulvovaginal, and 3 unknown primaries), PET/CT was able to detect residual primary disease, assess treatment response, and reveal or exclude metastases. Additional lesions compared to conventional imaging were found in five, while in one with brain metastases PET/CT was unable to detect lesions on MRI. Thirteen patients had negative PET/CT finding of which 11 (85%) did not have remarkable finding on follow-up. Metastatic disease was recognized in eight. Patients with extensive metastases on FDG PET/CT had a poorer outcome.

Conclusion: Similar to cutaneous melanoma, PET/CT is valuable in the management of NCM patients and is superior to conventional imaging modalities, with the exception of brain metastases. Patients with negative PET/CT findings have a better outcome as opposed to patients with significant positive PET/CT findings.

Keywords: Metastases; Non-cutaneous melanoma; PET/CT; Prognosis.

Figure 1

(A) FDG PET/CT of an 87-year-old male with noncutaneous melanoma (NCM) in the right nasal cavity with extension to adjacent sinuses (case 9). (B) FDG PET/CT of a 54-year-old male with NCM, presenting after resection of left parotid mass. (Additional metastatic lesion is noted in the right parotid, not recognized on patient’s CT scan, case 21). (C) A 40-year-old male with NCM of right tonsil. (FDG PET/CT reveals residual disease at the site of right tonsillectomy as well as metastatic lymph nodes in right cervical zone II, case15). (D) MIP image of a 74-year-old female with vulvar NCM revealing extensive metastases, case 20. (E) FDG PET/CT of a 66-year-old female with NCM in the anal canal (case 18). (F) FDG PET/CT image of a 32-year-old female with NCM of unknown primary currently revealing metabolically inactive sclerotic bone lesions in the site of previously lytic bone metastases, indicative of complete response to treatment (case 22). (G) FDG PET/CT image of the patient in MIP image (D), revealing local recurrence (case 20)