A multivariate analysis showed increased 5-year DSS among patients who received surgery (HR, 0.41; 95% CI, 0.30-0.56; P less than .001) and decreased 5-year DSS among patients over 50 (HR 3.27, 95% CI, 1.17-9.17; P = .02 for age 50-59).
“The prognostic factors are very similar, so you should treat these patients (with MUP) similarly to patients with melanoma of known primary, the same treatments, the same clinical trials,” Dr. Scott and associates said.
The results also raise the possibility of gaining a better understanding of how immune response affects the course of metastatic melanoma.
“If MUP is due to the fact that your immune system is attacking the primary tumor, then what characteristics of the person would cause that to happen? Are younger patients (exhibiting) a more robust immune response? Could that explain why their prognosis is better? More molecular studies of the actual tumors and the immune characteristics of these patients would help us answer that,” they added.
A resolved primary tumor isn’t the only explanation for MUP, however. It’s also possible that melanocytes are found in unexpected sites, perhaps because they did not complete their migration during development. “They could give rise to melanoma that would present (as MUP). Maybe there never was a skin tumor,” the authors wrote.
The investigators recommend a thorough search for a primary tumor, employing ophthalmologists, gynecologists, and other specialists if necessary. “You could argue that once you have metastatic disease, what’s the point of finding the primary tumor? But it’s important to correctly classify these patients, in terms of what clinical trials and treatments they may be eligible for,” Dr. Scott and associates said.
SOURCE: Scott JF et al. J Am Acad Dermatol. 2018 Mar 23. doi: 10.1016/j.jaad.2018.03.021.