Melanoma of Unknown Primary: Evaluation of the Characteristics, Treatment Strategies, Prognostic Factors in a Monocentric Retrospective Study

Abstract

BackgroundMelanoma of unknown primary (MUP), accounts for up to 3% of all melanomas and consists of a histologically confirmed melanoma metastasis to either lymph nodes, (sub)cutaneous tissue, or visceral sites without any evidence of a primary cutaneous, ocular, or mucosal melanoma. This study aimed to investigate the characteristics, treatment strategies, and prognostic factors of MUP patients, in order to shed some light on the clinical behavior of this malignancy.MethodsAll the consecutive patients with a diagnosis of MUP referring to our institutions between 1985 and 2018 were considered in this retrospective cohort study. The records of 173 patients with a suspected diagnosis of MUP were retrospectively evaluated for inclusion in the study. Patient selection was performed according to the Das Gupta criteria, and a total of 127 MUP patients were finally included in the study, representing 2.7% of the patients diagnosed with melanoma skin cancer at our institutions during the same study period. A second cohort of all consecutive 417 MKP patients with AJCC stages IIIB–IV, referring tions in the period considered (1985–2018), was included in the study to compare survival between MUP and MKP patients. All the diagnoses were based on histopathologic, cytologic and immunohistochemical examination of the metastases. All tumors were re-staged according to the 2018 American Joint Committee on Cancer (AJCC) 8th Edition.ResultsMedian follow-up was 32 months (IQR: 15–84). 3-year progression-free survival (PFS) was 54%, while 3-year overall survival (OS) was 62%. Worse OS and PFS were associated with older age (P = 0.0001 for OS; P = 0.008 for PFS), stage IV (P < 0.0001 for OS; P = 0.0001 for PFS) and higher Charlson Comorbidity Index (P < 0.0001 for OS and P = 0.01 for PFS). Patients with lymph node disease showed longer PFS (P = 0.001) and OS (P = 0.0008) than those with (sub)cutis disease. Complete lymph node dissection (CLND) was the most common surgical treatment; a worse OS in these patients was associated with the number of positive lymph nodes (P = 0.01), without significant association with the number of retrieved lymph nodes (P = 0.79). Survival rates were lower in patients undergoing chemotherapy (CT) and target therapy (TT), and higher in those receiving immunotherapy (IT). 417 patients with AJCC stages IIIB–IV of Melanoma Known Primary (MKP) were included for the survival comparison with MUP. 3-year PFS rates were 54 and 58% in MUP and MKP, respectively (P = 0.30); 3-year OS rates were 62 and 70% in MUP and MKP, respectively (P = 0.40).ConclusionsThe most common clinical scenario of our series was a male patient around 59 years with lymph node disease. We report that CLND associated with IT was the best treatment in terms of survival outcome. In the current era of IT and TT for melanoma, new studies have to clarify the impact of novel drugs on MUP.

Treatment of Metastatic Melanoma at First Diagnosis: Review of the Literature

“…This study analyzed the characteristics and the different therapeutic modalities established in 127 patients, comparing them with MPK patients. No differences were found between the survival rates of patients treated with immunotherapy or with targeted therapy [57]. Despite being the study with the largest number of patients, the authors highlight the heterogeneity of the population and the therapeutic strategies received, so further studies are needed to confirm their conclusions.…”

A rare case of endobronchial melanoma of unknown primary

“…A meta-analysis also found better survival outcomes in patients with MUP than in those with a known primary at the same corresponding stage [ 23 ]. It can be speculated that the absence of primary cutaneous melanoma translates into lesser tumor burden and better prognosis [ 4 ]. In addition, MUP may have a different biology that initially induced the regression of the primary lesion, favoring a better prognosis [ 24 ].…”

“…Melanoma of unknown primary (MUP) is a histologically confirmed melanoma metastasis to the lymph nodes, subcutaneous tissue, or visceral organs, occurring without any known primary lesion [ 3 ]. MUP accounts for up to 3% of all melanomas [ 4 , 5 ], among which nodal metastasis is the most common (approximately 40–60% of all cases), followed by subcutaneous metastasis (approximately 30% of cases) [ 6 ]. Visceral organs are the least commonly diagnosed MUP sites and endobronchial MUPs are particularly rare [ 7 ].…”

PET/CT variants and pitfalls in malignant melanoma

“…Approximately 3% of metastatic melanomas are of unknown primary [ 6 ]. This potentially reflects spontaneous regression of the primary as a result of innate immune responses.…”