Molecular Mechanisms in Melanoma: Investigating the Role of MicroRNAs

Background: [18F]F-FDG PET-CT is a key imaging test for staging and detection of metastases in melanoma.False positives, although rare, can occur.Methods: Retrospective single-center case series.We present two patients with cutaneous uptake on [18F]F-FDG PET-CT suggestive of metastasis, with histopathological examination revealing benign processes.Results: Case 1 73-year-old woman diagnosed with melanoma of the scalp (Breslow 3.7 mm) with satellitosis and bilateral cervical lymph node involvement (Stage IIIC).During follow-up after treatment, a control PET-CT scan showed two foci uptake in the middle third of the left leg (SUVmax 10.45).Skin ultrasound revealed septal hyperechogenicity in the subcutaneous tissue and after excision of the lesion, the histopathological diagnosis revealed erythema nodosum.Case 2: 56-year-old man with nodular melanoma on the back (Breslow 1.75 mm) and left inguinal involvement (Stage IIIC).The patient was in complete remission after adjuvant treatment with nivolumab.A follow-up PET-CT scan detected a subcutaneous lesion uptake on the left back (SUVmax 3.16).Excision of the lesion led to a diagnosis of pilomatricoma.Discussion: PET-CT is highly sensitive and specific for stage III and IV melanoma, but false positives can occur, especially in cutaneous lesions.This may lead to invasive procedures and affect patients psychologically, as it is difficult to ascertain the nature of the lesions with other non-invasive techniques.False positive rates in melanoma patients range from 5.8% to 9.6%.[1] The skin is one of the most common sites for these false positives, having been described in relation to sarcoidosis, infected cysts, erythema nodosum, Kikuchi-Fujimoto disease or acne vulgaris, among others.[2]Of note is our patient with a pilomatricoma which, being a benign tumor, presented a suspicious hypermetabolism, unlike the lesions previously described in relation to inflammatory processes.Conclusions: Knowing the possible causes of false positives is crucial to avoid misdiagnosis and its implications for treatment.This underlines the importance of improving diagnostic protocols and radiological technologies to optimise accuracy in the use of PET-CT, as well as the importance of histological diagnosis for the proper management of these patients.