Track: Case Reports

Topic: Melanocytic Neoplasms

Abstract:

Spitzoid melanoma, subtype of melanoma, clinicopathologically resembles Spitz nevus, with differentiation based on morphology and molecular landscape. We present a 15-year-old male with metastatic Spitzoid melanoma progressing in a previously excised nevus diagnosed as Spitz nevus to illustrate potential pitfalls and the value of genomic confirmation. A nevus on his left cheek was removed by two resections due to positive margins, with a pathology consistent with inflamed compound Spitz nevus. Without regular follow-up, enlarged left cervical lymph nodes were found 2 years later, and pathology confirmed metastatic melanoma. Patient received neoadjuvant immunotherapy with trametinib and dabrafenib for 6 months followed by lymph node resection, with pathology revealing 2/24 nodes positive to melanoma. He then received another 6 months of this therapy without hypermetabolic lymphadenopathy by PET scan. After one-year follow-up, he was found to have numerous lymphadenopathies on left and right neck on PET scan. Initial biopsies showed reactive nodes, but subsequent biopsy identified metastatic melanoma with TMB of 24 muts/Mb including BRAF V600E, TP53 and TERT promoter mutation which defined the Spitzoid melanoma. Mutation pattern was found to be consistent with DNA mismatch repair deficiency mutation signature. PD-L1 expression in tumor cells was present (30%). Pembrolizumab was started for one year and patient has had a complete remission with a close follow-up with repeated PET scan every 3 – 6 months. This case raises the awareness of the role of genetic testing in differentiation between Spitz melanocytic proliferation and melanoma with Spitzoid features (or Spitzoid melanoma) that requires close monitoring.

Tung Tran

Affiliation

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(245) Molecularly confirmed metastatic melanoma of Spitzoid features with high tumor mutation burden, DNA mismatch repair deficiency mutation signature and significant response to PD-1 inhibitor