Spitz tumors are a tricky type of skin growth. Most are harmless, but some can behave like melanoma. Now, a new analysis of 144 cases finds that the specific gene fusion driving the tumor may help tell them apart.
Researchers looked at Spitz tumors with ALK gene fusions. They found six main patterns under the microscope, from wavy spindle cells to nevus-like shapes. Each pattern was linked to a different fusion partner gene. For example, tumors with a TPM4 fusion often looked like Reed-Spitz nevi, while those with EHBP1 were mostly epithelioid. These links were statistically significant.
The study also identified features tied to worse outcomes: extra copies of the c-MYC gene, loss of the CDKN2A gene, and a higher mitotic count (5.5 per mm2 in metastatic cases vs 2.2 in nonmetastatic). This is the first large look at how ALK fusion partners relate to tumor appearance and behavior.
But this is an observational study, so it can't prove cause and effect. The findings need to be confirmed in larger, prospective studies. Still, they offer doctors more clues to spot which Spitz tumors might need closer attention.