Decoding Melanoma of Unknown Primary: Genetics and Survival

Melanoma of unknown primary accounts for approximately 10% of all metastatic melanoma cases. However, identifying the exact origin of these tumors has historically challenged oncologists. A recent multicentre study from the DeCOG registry provides new clarity on the nature of melanoma of unknown primary. Researchers discovered that these tumors share a distinct oncogenic pattern with sun-exposed cutaneous melanoma. This finding suggests that most cases likely originate from regressed or occult skin lesions.

Genetic Profiles and the UV Signature in Melanoma of Unknown Primary

The study utilized next-generation sequencing to examine the genetic landscape of MUP patients. Interestingly, the genetic analysis revealed a clear ultraviolet (UV) mutation signature. This evidence strongly suggests that these tumors arise from sun-exposed locations, even if the primary site remains missing. Furthermore, the research team detected TERT promoter mutations in 66.4% of the analyzed samples. Additionally, activating mutations in BRAF V600E and NRAS occurred in 39.1% and 33.6% of patients, respectively. Specifically, the prevalence of these mutations mirrors the patterns seen in common skin cancers. These results provide a molecular basis for understanding the progression of metastatic disease in patients without a visible primary lesion.

Comparison of Clinical Outcomes

Clinicians frequently evaluate whether the absence of a primary tumor influences patient survival. Consequently, researchers compared survival outcomes between MUP and known cutaneous primary (MKP) cohorts. The results showed that overall survival at 48 months was 65% for MUP patients. Notably, after adjusting for age, sex, and tumor stage, survival rates remained comparable across both groups. This evidence supports the use of standard melanoma management protocols for MUP cases. Therefore, healthcare providers can offer similar treatment pathways and prognostic expectations for both patient populations.

Frequently Asked Questions

Is the prognosis for melanoma of unknown primary worse than cutaneous melanoma?

No, research shows that when adjusted for age and stage, overall survival for melanoma of unknown primary is comparable to melanoma of known cutaneous primary.

What does a UV signature in MUP imply?

A UV signature suggests that the melanoma likely originated in sun-exposed skin areas, even if the primary lesion remained unrecognized or underwent spontaneous regression.

Which genetic mutations are most common in MUP?

The most common genetic alterations in melanoma of unknown primary include TERT promoter mutations, along with BRAF and NRAS mutations, which are characteristic of sun-damaged skin.

Disclaimer: This content is for informational and educational purposes only and does not constitute medical advice or a professional relationship. Refer to the latest local and national guidelines for clinical practice.

References

Lodde G et al. Melanoma of unknown primary shows oncogenic pattern and clinical course of sun-exposed melanoma. Br J Dermatol. 2026 Feb 20. doi: undefined. PMID: 41719057.

Bae JY et al. Overall Survival of Patients with Melanoma of Unknown Primary Versus Melanoma of Known Primary: A Systematic Review and Meta-Analysis. MDPI. 2025 Aug 22.

Wu D et al. Melanoma of unknown primary: a comprehensive review of immune-mediated pathogenesis and therapies. The Oncologist. 2026 Jan 1;31(1):3-15.