SAN DIEGO – As with many markers for the evaluation of challenging melanocytic lesions, preferentially expressed antigen in melanoma (PRAME) has its benefits and drawbacks, according to Cora Humberson, MD.
"I'm a fan, but there are issues with it," Dr. Humberson, dermatopathology coordinator in the department of pathology at Scripps MD Anderson Cancer Center, San Diego, said at the annual Cutaneous Malignancy Update. "It's all in how you use it."
PRAME is part of the cancer/testis (CT) antigens, of which more than 40 have now been identified. They are encoded by genes that are normally expressed only in the human germ line, but are also expressed in various tumor types, including melanoma and carcinomas of the bladder, lung, and liver. "The biological function of these antigens is not fully understood, but they may act as a repressor of retinoic acid, potentially inhibiting differentiation, inhibiting proliferation arrest – things that we associate with malignancy," she said at the meeting, which was hosted by Scripps MD Anderson Cancer Center. "These immunogenic proteins are being pursued as targets for therapeutic cancer vaccines," she noted.
CT antigens are also being evaluated for their role in oncogenesis, she added. Recapitulation of portions of the germline gene-expression might contribute characteristic features to the neoplastic phenotype, including immortality, invasiveness, immune evasion, and metastatic capacity.
According to Dr. Humberson, PRAME can be used to differentiate comingled nevus and melanoma, to distinguish between nevoid melanoma and nevus, and for melanoma margin assessment in sun-damaged skin. One potential pitfall is that sun-damaged melanocytes may express PRAME. "The older the person and the more sun damage [they have], the more likely you are to see this, but the melanocytes won't be grouped, they'll be scattered," she said.
Another pitfall is that less than 15% of nevi may express PRAME. "PRAME can be expressed in scars, so if you're looking at a spindle cell lesion, be aware that you might be looking at a scar if you're seeing PRAME expression," she added. She also noted that PRAME immunohistochemistry (IHC) expression is not a prognostic biomarker in thin melanomas.
If fewer than 25% of cells in a melanocytic lesion express PRAME, most published assessments of PRAME IHC favor nevi as the diagnosis. "If more than 75% are expressing it, it favors melanoma," Dr. Humberson said. "There's a big category in between. It's not that 30% is more likely benign or that 60% is more likely malignant; you can't really depend upon [PRAME] if you're in this range."
A diagnostic accuracy study found that when more than 75% of cells express PRAME, the marker has a sensitivity of 0.63 and a specificity of 0.97.
Selected PRAME-related published references she recommended include: J Cutan Pathol. 2021;48(9):1115-23; Diagnostics. 2022 Sep 9; 12(9):2197, and J Cutan Pathol. 2022;49(9):829-32.
Dr. Humberson reported having no relevant disclosures.
This article originally appeared on MDedge.com, part of the Medscape Professional Network.
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Image 1: Scripps MD Anderson Cancer Center
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Cite this: How Should PRAME Be Used to Evaluate Melanocytic Lesions? - Medscape - Jan 27, 2023.