Melanoma of unknown primary associated with similar survival as cutaneous primary

Despite more frequent poor prognostic factors, melanoma of unknown primary etiology was not associated with poorer survival than melanoma of known cutaneous etiology, according to a study.

“Clinical outcomes of advanced melanoma of unknown primary in the era of novel therapies have been scarcely studied,” Perrine Rousset, MD, of the dermatology department at the University Hospital of Nice in France, and colleagues wrote.

The study used data from the French nationwide MelBase database to assess the efficacy and safety of systemic therapies in patients with melanoma of unknown primary etiology. These findings were then compared with staged-matched data for patients with melanoma with known cutaneous primary etiology.

The analysis included 1,882 patients (median age, 66 years; interquartile range [IQR], 18-97; 60% men) treated between March 2013 and June 2021. There were 265 patients with melanoma of unknown primary included.

Eligible participants underwent treatment with first-line immunotherapies (65%), targeted therapies (31%) or chemotherapy.

Progression-free survival and overall survival served as the co-primary endpoints. The researchers also assessed for treatment-associated toxicity.

Patients in the unknown primary group were followed for a median of 11 months (IQR, 4.5-21.1), whereas those in the cutaneous primary group were followed for 16.3 months (IQR, 6.2-33.3).

Unfavorable initial prognostic factors were more commonly observed in the unknown primary group compared with cutaneous primary group. For example, stage IV disease was reported in 97% of unknown primary cases compared with 85% of cutaneous primary cases (P < .001). In addition, patients in the unknown primary group had a higher number of metastatic sites (48% vs. 39% for patients with three or more metastatic sites; P = .01).

Further data showed that central nervous system metastases were reported in 38% of patients in the unknown primary arm and just 18% of those in the cutaneous primary arm (P < .001), whereas elevated lactate dehydrogenase levels were also higher in the unknown primary group (12% vs. 8%; P = .01).

However, progression-free survival and overall survival rates were not statistically different between the two arms.

Treatment-related toxicity rates were also similar, as was the severity of those events.

“Although patients with [melanoma of unknown primary] had less favorable baseline prognostic factors, they benefited from the novel therapies as much as those with [melanoma of known cutaneous primary],” the researchers concluded. “They should be managed according to similar strategies.”